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Ibee  p.  99 


OF     THE     SKY 







ETC.     ETC. 





THE   MOON   METAL.     Post  8vo 

Illustrated.     Post  8vo 

CURIOSITIES  OF   THE   SKY.     Illustrated.     8vo 

Illustrated.     8vo 
ELOQUENCE.    Post  8vo 


Copyright,  1909,  by  HARPER  &  BROTHERS. 

Published  November,  1909. 
Printed  in  the  United  States  of  America 




On  the  edges  of  the  universe — The  mystery  of  the  "  Coal-sacks" — 
Description  of  the  great  "Coal-sack"  in  the  "Southern  Cross" 
— Its  effect  upon  the  imagination — The  "Coal-sack"  in  Cygnus 
— Photographic  discovery  of  apparent  apertures  in  the  Milky 
Way — Strange  lanes  among  the  stars — Professor  Barnard's 
theory  of  "Dark  Nebulae"  —  The  problem  of  the  extinction 
of  light  in  space — If  the  "Coal -sacks"  are  openings  in  the  walls 
of  the  universe,  what  lies  beyond? — Inconceivability  of  an 
end  to  space — The  universe  not  a  Crusoe  lost  in  immensity — 
Reasons  for  thinking  that  other  universes  exist — What  is  their 
probable  appearance? — Will  any  of  them  ever  be  seen  from 
our  starry  system? — Does  the  luminiferous  ether  extend 
throughout  infinite  space? Page  i 


The  Milky  Way  the  most  stupendous  of  all  astronomical  phe- 
nomena— The  strange  ground-plan  of  the  universe — A  chaplet 
of  a  hundred  million  suns — An  extraordinary  speculation  con- 
cerning the  nature  of  the  Galaxy — Professor  Comstock's  "star- 
plough" — The  wonderful  details  of  the  Milky  Way — Distinc- 
tion between  star-clouds,  star-swarms,  and  star-clusters — The 
mystery  of  the  globular  star-clusters — The  "  Great  Cluster  in 
Hercules"  and  the  still  richer  one  in  Centaurus — How  did  the 
stars  in  dense  clusters  come  together  ? — The  startling  idea  of  an 
explosion — The  wonderful  association  of  stars  and  nebulas 
in  the  Pleiades — Nebulous  "rail  fences"  with  strange  banks 
of  stars  arrayed  along  them  ........  Page  17 




The  paradox  of  the  "  fixed  stars" — All  is  motion  in  the  universe — 
Extraordinary  speed  of  some  "runaway  stars" — The  fearful 
momentum  of  Arcturus — What  is  to  become  of  stars  whose 
motion  is  so  swift  that  the  attractions  of  the  universe  cannot 
govern  them? — Stars  travelling  in  groups — The  motion  of  the 
solar  system — Whence  have  we  come,  and  whither  do  we  go? 
— Enormous  spaces  that  the  earth  has  traversed  during  the 
geologic  ages — Curious  thoughts  suggested  by  this  stupendous 
voyage — Shall  we  eventually  join  the  Milky  Way? — The  ex- 
traordinary theory  of  a  double  drift  of  the  stars — Is  the  stellar 
system  divided  into  two  opposed  streams? — Stars  moving  like 
snow-flakes  driven  before  interpenetrating  winds  .  .  Page  39 


How  time  affects  the  blazonry  of  the  heavens — The  constellations 
and  human  tradition — The  most  lasting  records  of  men's 
thoughts — The  constellations  and  religion — American  tradi- 
tions— The  wonderful  impression  made  by  Greek  tradition  as 
preserved  in  the  stars — The  effects  of  the  stellar  motions  in 
difforming  the  constellations— When  the  "Great  Dipper" 
will  no  longer  hold  water — Curious  results  of  star-drift  in  the 
"Northern  Crown"  —  The  Hyades  drifting  apart  —  Famous 
star  figures,  full  of  poetic  suggestion,  which  cannot  last — Orion, 
the  "  Mighty  Hunter,"  stands  almost  unchanged,  but  his  "  belt" 
is  falling  to  pieces — The  curious  fate  that  attends  the  beautiful 
"Southern  Cross" — Future  mythologies  must  invent  new 
constellations — The  sun  among  the  constellations  seen  from 
distant  space Page  53 


The  burning  up  of  the  earth  would  be  a  catastrophe  invisible 
from  stellar  space — Yet  many  great  outbursts  of  light  have 
appeared  to  us  among  the  stars — The  phenomena  of  new  or 
temporary  stars — The  famous  star  of  Tycho — The  legend  that 



it  was  a  reappearance  of  the  "Star  of  Bethlehem" — Kepler's 
star,  and  other  fiery  outbursts — The  great  new  star  of  1901, 
"Nova  Persei,"  and  the  light  it  has  thrown  on  such  phenomena 
— Extraordinary  theories  based  upon  it — Was  it  the  result  of  a 
collision  ? — How  suns  may  be  a  source  of  danger  to  each  other 
without  coming  into  actual  collision — The  theory  of  an  en- 
counter between  a  star  and  a  "dark  nebula" — Suggestion  of 
the  "running  down"  of  planets  by  an  invading  star — Janssen's 
theory  of  explosive  chemical  action — How  temporary  stars 
appear  to  run  through  the  stages  of  stellar  history  in  a  few 
months — Significance  of  their  changes  of  color.  .  Page  68 


Professor  Keeler's  surprising  discovery  that  most  of  the  nebulas 
are  spiral  in  form — The  effect  of  this  discovery  on  Laplace's 
Nebular  Hypothesis — Immense  variety  of  the  spiral  forms — 
Is  Laplace's  hypothesis  still  applicable,  with  modifications,  to 
our  particular  system?  —  Suggestive  forms  of  "rings"  and 
"  planetary  "  nebulae — The  marvels  revealed  by  photography 
in  Lord  Rosse's  "  Whirlpool,"  and  the  amazing  spectacle  pre- 
sented by  a  spiral  nebula  in  Triangulum — Other  strange 
forms — The  wonderful  Andromeda  Nebula — The  mystery  of 
the  "white"  nebulae — The  chaotic  gaseous  nebula  in  Orion — 
Suggestive  arrangement  accompanying  stars — Are  these  nebulae 
the  birthplaces  of  star-clusters? — The  new  " Planetesimal  Hy- 
pothesis," and  the  astonishing  view  of  the  origin  of  solar  sys- 
tems that  it  offers — Do  we  yet  know  the  real  truth  ?  .  Page  88 


The  wonderful  surroundings  of  the  sun  that  only  an  eclipse  re- 
veals— The  dramatic  story  of  the  first  scientific  observation  of 
the  corona  and  the  prominences  of  the  sun  —  The  coronas  of 
1900  and  1905 — The  curved  rays  about  the  solar  poles  resem- 
bling the  lines  of  force  of  a  magnet — Solar  magnetic  influence 
upon  the  earth — The  phenomena  of  the  eruptive  prominences 
— Does  the  sun  hurl  forth  masses  of  matter  that  reach  the 
planets? — Connection  of  the  prominences  and  the  corona  with 
sun-spots — The  remarkable  results  of  the  "pressure  of  light" — 
The  sun-spot  period  and  "magnetic  storms" — The  sun  a 



variable  star — How  its  light  is  partially  cut  off  by  absorbing 
vapors — Once  it  probably  shone  more  brilliantly  than  it  does 
at  the  present  time Page  113 


The  ghostly  presence  that  towers  above  the  sunken  sun — The 
light  varies  in  appearance  with  the  seasons — How  it  looks  in 
the  tropics  and  upon  the  equator — Humboldt's  observations — 
The  Zodiacal  Light  in  1909 — The  writer's  observations — The 
curious  "Gegenschein" — Professor  Barnard's  observations — The 
Rev.  Mr.  Jones'  round  the  world  studies  of  the  Zodiacal  Light 
— The  extraordinary  theory  of  Arrhenius — Once  more  the 
pressure  of  light — How  negatively  charged  corpuscles  driven 
from  the  sun  are  conceived  to  envelop  the  earth  and  produce 
the  appearance  of  the  Zodiacal  Light — The  theories  of  coronal 
extension  and  of  clouds  of  meteors — Why  an  airless  planet 
cannot  have  comets'  tails  as  the  earth  is  supposed  to 
have Page  131 


An  amazing  spectacle  that  recalled  pictures  of  "The  Day  of 
Judgment" — The  aurora  of  1882,  and  the  strange  upright 
beam  that  appeared  stalking  across  the  sky — Auroras  in  the 
Arctic  and  Antarctic  regions — Their  connection  with  the 
magnetic  poles — The  earth  as  a  great  magnet — Astonishing 
phenomenon  observed  in  1859 — Outbursts  on  the  sun  followed 
by  extraordinary  auroral  displays  and  magnetic  storms  on  the 
earth — Lord  Kelvin's  objection,  and  the  answer  to  it — Proofs 
of  the  intimate  connection  between  solar  outbreaks  and  terres- 
trial disturbances — Another  application  of  the  theory  of 
Arrhenius — Negative  particles  shot  from  the  sun  supposed  to 
electrify  the  earth's  atmosphere  and  thus  to  produce  the 
play  of  the  auroral  lights — Curious  confirmations  of  the 
theory Page  144 


How  the  fears  and ,  superstitions  of  ancient  times  have  been  suc- 
ceeded by  scientific  study  of  comets — An  account  of  the 



characteristic  phenomena  of  a  comet — Science  itself  has  dis- 
covered mysteries — How  the  nuclei  and  tails  of  comets  are 
developed — The  chemical  constituents  of  comets — Remarkable 
comets  of  the  nineteenth  century  —  The  monster  of  space  that 
looked  at  us  afar  off  in  1729 — The  great  comet  of  i8n,  and 
its  enormous  tail — In  1843  a  comet  was  visible  in  broad  day 
beside  the  sun — The  beautiful  comet  of  1858,  and  its  supposed 
connection  with  the  wine  crop — Astonishing  association  of 
the  comets  of  1843,  1880,  and  1882 — Three  pieces  of  one  orig- 
inal mass  —  The  disintegration  of  the  head  of  the  comet  of 
J882 — Professor  Forbes'  theory  that  these  comets  were  split 
up  by  the  action  of  a  yet  undiscovered  planet  beyond  Neptune — 
Strange  adventures  of  Lexell's  comet — Arrhenius'  theory  of 
the  origin  of  comets'  tails — Driven  off  by  the  pressure  of  light — 
Jupiter  as  the  great  comet-catcher — Do  comets  ever  come  into 
the  solar  system  from  interstellar  space,  or  are  they  originally 
carried  along  in  the  same  "  current"  that  bears  onward  the  sun 
and  the  planets? Page  165 


The  terrorizing  spectacle  of  1833  and  its  connection  with  a  dis- 
integrated comet — The  "umbrella  of  fire"  and  the  light  that 
it  cast  on  the  meaning  of  the  amazing  display — Olmstead's  and 
Schiaparelli's  investigations  —  Meteor-swarms  travel  in  the 
tracks  of  comets — The  tragic  fate  of  Biela's  comet — Why  the 
November  spectacle  failed  in  1899 — The  distinction  between 
meteors  and  meteorites — Stone  meteorites  and  iron  meteorites 
— Former  incredulity  of  men  of  science  concerning  stones  fall- 
ing from  the  sky — Showers  of  stones — Famous  meteorites  of 
ancient  times — Nickel-iron  from  the  sky — Diamonds  in  me- 
teorites— Do  such  bodies  come  from  the  sun  or  the  stars,  or 
have  they  been  shot  out  from  lunar  volcanoes? — The  mystery 
of  Coon  Butte — Was  the  crater  in  Arizona  made  by  a  falling 
meteorite? Page  186 


A  "fossil  world"  in  the  sky — Unique  character  of  the  lunar 
scenery — The  story  of  disaster  that  the  moon  carries  sculptured 



on  its  face — Gigantic  size  of  the  craters  of  the  moon — How 
they  differ  from  the  volcanic  craters  of  the  earth — Some  strik- 
ing comparisons  of  magnitude — How  the  slight  force  of  lunar 
gravity  may  account  for  the  gigantic  dimensions  of  the  craters 
— The  theory  that  they  may  have  been  formed  by  meteoric 
impact — The  question  of  former  life  on  the  moon — The  uni- 
versality of  the  destruction  wrought  by  the  volcanoes — The 
puzzle  of  the  ancient  sea  beds — Were  they  once  floods  of  molten 
lava? — Mr.  Ritchey's  wonderful  photographs  and  their  revela- 
tions— Suggestions  of  a  double  tragedy  in  the  career  of  the 
lunar  world — Ruin  beneath  ruin  recalling  the  strata  of  buried 
cities  in  the  mound  of  ancient  Troy Page  213 


Life  not  ubiquitous,  though  probably  present  in  all  quarters  of 
the  universe — The  life  question  in  the  solar  system — Why  Mars 
has  been  selected  as  the  most  probable  abode  of  life  among 
the  other  planets — The  principal  facts  known  about  Mars — 
Its  singular  resemblances  to  the  earth,  and  its  no  less  remark- 
able differences  from  our  planet — The  discoveries  of  Schiaparelli 
and  Lowell — The  problematical  "canals,"  their  peculiarities, 
and  the  interpretation  that  has  been  put  upon  them — Mars 
a  half-dried-up  world — The  wonderful  struggle  to  retain  life 
which  is  ascribed  to  its  inhabitants — Their  possibly  gigantic 
size,  and  the  reasons  which  have  been  given  for  thinking  that 
they  may  be  more  advanced  than  we  are — Mr.  Lowell's  theory 
of  life  on  Mars — Public  works  that  put  the  utmost  achieve- 
ments of  man  to  shame — Objections,  and  the  answers  to 
them Page  237 


A  ring  of  little  worlds  where  astronomers  expected  to  find  a  single 
large  one — Olbers'  startling  hypothesis  of  a  planetery  explosion 
— Measures  of  the  four  largest  asteroids — The  objections  to  the 
explosion  hypothesis,  and  the  support  which  it  seems  to  derive 
from  the  probable  abnormal  shapes  of  Eros  and  others — 
The  theory  of  a  series  of  explosions — How  could  a  world  ex- 
plode?— Evidences  of  explosive  forces  in  nature — The  ex- 



traordinary  ideas  of  Doctor  Le  Bon  concerning  the  results  of 
atomic  disintegration — The  phenomena  of  the  radium  group  of 
elements  appealed  to  in  support  of  the  hypothesis  that  worlds 
may  blow  up  when  they  have  grown  very  old — This,  says 
Doctor  Le  Bon,  may  represent  the  most  general  ending  of  the 
bodies  composing  the  universe Page  254 

INDEX 265 



THE    MILKY    WAY Facing  p.        4 

STAR-CLUSTER    IN    HERCULES "            26 

GREAT  SOUTHERN   STAR-CLUSTER,   OMEGA  CENTAURI      .  "            30 

THE    PLEIADES "             34 

THE  "GREAT  DIPPER" Page      58 

CASSIOPEIA "        60 

THE  "NORTHERN  CROWN"       "        63 

THE  "SOUTHERN  CROSS" "        65 


NOVA   PERSEI    OF    IQOI Facing  p.     70 

NOVA    PERSEI,    WITH    ITS    NEBULAR   RINGS          .      .       .       .  "            80 

LORD    ROSSE'S    NEBULA "            88 

WONDERFUL    SPIRAL   IN    TRIANGULUM "            92 

SPIRAL   IN    URSA    MAJOR          96 



THE    CORONA 1 14 





AURORAL   CURTAIN    SEEN    IN    SCANDINAVIA        ....  154 

AURORAL   ARCHES    SEEN    IN    SCANDINAVIA "         160 




DANIELS'  COMET Facingp.  176 

BROOKS'  COMET "  180 





RIM *'  204 

TRAIL   ON    SOUTH    SIDE,    COON    BUTTE    CRATER      ..."  2o8 


WESTERN   PART   OF  THE  MARE   SERENITATIS       ....  '*  222 



MARE    CRISIUM "  234 


OP    SO-CALLED    CANALS "  244 


WHAT  Froude  says  of  history  is  true  also  of 
astronomy:  it  is  the  most  impressive  where  it 
transcends  explanation.  It  is  not  the  mathematics 
of  astronomy,  but  the  wonder  and  the  mystery  that 
seize  upon  the  imagination.  The  calculation  of  an 
eclipse  owes  all  its  prestige  to  the  sublimity  of  its 
data;  the  operation,  in  itself,  requires  no  more  mental 
effort  than  the  preparation  of  a  railway  time-table. 

The  dominion  which  astronomy  has  always  held 
over  the  minds  of  men  is  akin  to  that  of  poetry;  when 
the  former  becomes  merely  instructive  and  the  latter 
purely  didactic,  both  lose  their  power  over  the  imag- 
ination. Astronomy  is  known  as  the  oldest  of  the 
sciences,  and  it  will  be  the  longest-lived  because  it  will 
always  have  arcana  that  have  not  been  penetrated. 

Some  of  the  things  described  in  this  book  are  little 
known  to  the  average  reader,  while  others  are  well 
known;  but  all  possess  the  fascination  of  whatever  is 
strange,  marvellous,  obscure,  or  mysterious — magni- 
fied, in  this  case,  by  the  portentous  scale  of  the 

The  idea  of  the  author  is  to  tell  about  these  things 
in  plain  language,  but  with  as  much  scientific  accuracy 



as  plain  language  will  permit,  showing  the  wonder 
that  is  in  them  without  getting  away  from  the  facts. 
Most  of  them  have  hitherto  been  discussed  only  in 
technical  form,  and  in  treatises  that  the  general 
public  seldom  sees  and  never  reads. 

Among  the  topics  touched  upon  are:  The  strange 
unfixedness  of  the  "fixed  stars,"  the  vast  migrations 
of  the  suns  and  worlds  constituting  the  universe; 
The  slow  passing  out  of  existence  of  those  collocations 
of  stars  which  for  thousands  of  years  have  formed 
famous  "  constellations,"  preserving  the  memory  of 
mythological  heroes  and  heroines,  and  perhaps  of 
otherwise  unrecorded  history;  The  tendency  of  stars 
to  assemble  in  immense  clouds,  swarms,  and  clusters; 
The  existence  in  some  of  the  richest  regions  of  the 
universe  of  absolutely  black,  starless  gaps,  deeps, 
or  holes,  as  if  one  were  looking  out  of  a  window  into 
the  murkiest  night;  The  marvellous  phenomenon  of 
new,  or  temporary,  stars,  which  appear  as  suddenly 
as  conflagrations,  and  often  turn  into  something  else 
as  eccentric  as  themselves;  The  amazing  forms  of  the 
"whirlpool,"  "spiral,"  "pinwheel,"  and  "lace,"  or 
"tress,"  nebulae;  The  strange  surroundings  of  the  sun, 
only  seen  in  particular  circumstances,  but  evidently 
playing  a  constant  part  in  the  daily  phenomena  of 
the  solar  system;  The  mystery  of  the  Zodiacal  Light 
and  the  Gegenschein;  The  extraordinary  transforma- 
tions undergone  by  comets  and  their  tails ;  The  prodi- 
gies of  meteorites  and  masses  of  stone  and  metal 
fallen  from  the  sky;  The  cataclysms  that  have 
wrecked  the  moon;  The  problem  of  life  and  intelli- 
gence on  the  planet  Mars;  The  problematical  origin 



and  fate  of  the  asteroids;  and  The  strange  phenom- 
ena of  the  auroral  lights. 

An  attempt  has  been  made  to  develop  these  topics 
in  an  orderly  way,  showing  their  connection,  so  that 
the  reader  may  obtain  a  broad  general  view  of  the 
chief  mysteries  and  problems  of  astronomy,  and  an 
idea  of  the  immense  field  of  discovery  which  still  lies, 
almost  unexplored,  before  it. 




most  minds  mystery  is  more  fascinating  than 
science.  But  when  science  itself  leads  straight 
up  to  the  borders  of  mystery  and  there  comes  to  a 
dead  stop,  saying,  "At  present  I  can  no  longer  see 
my  way,"  the  force  of  the  charm  is  redoubled.  On 
the  other  hand,  the  illimitable  is  no  less  potent  in 
mystery  than  the  invisible,  whence  the  dramatic 
effect  of  Keats'  "stout  Cortez"  staring  at  the  bound- 
less Pacific  while  all  his  men  look  at  each  other  with  a 
wild  surmise,  "silent  upon  a  peak  in  Darien."  It  is 
with  similar  feelings  that  the  astronomer  regards 
certain  places  where  from  the  peaks  of  the  universe 
his  vision  seems  to  range  out  into  endless  empty 
space.  He  sees  there  the  shore  of  his  little  isthmus, 
and,  beyond,  unexplored  immensity. 

The  name,  "coal -sacks,"  given  to  these  strange 
voids  is  hardly  descriptive.  Rather  they  produce 
upon  the  mind  the  effect  of  blank  windows  in  a  lonely 
house  on  a  pitch-dark  night,  which,  when  looked  at 
from  the  brilliant  interior,  become  appalling  in  their 


rayless  murk.  Infinity  seems  to  acquire  a  new  mean- 
ing in  the  presence  of  these  black  openings  in  the  sky, 
for  as  one  continues  to  gaze  it  loses  its  purely  meta- 
physical quality  and  becomes  a  kind  of  entity,  like 
the  ocean.  The  observer  is  conscious  that  he  can 
actually  see  the  beginning  of  its  ebon  depths,  in 
which  the  visible  universe  appears  to  float  like  an  en- 
chanted island,  resplendent  within  with  lights  and 
life  and  gorgeous  spectacles,  and  encircled  with 
screens  of  crowded  stars,  but  with  its  dazzling  vistas 
ending  at  the  fathomless  sea  of  pure  darkness  which 
encloses  all. 

The  Galaxy,  or  Milky  Way,  surrounds  the  borders 
of  our  island  in  space  like  a  stellar  garland,  and  when 
openings  appear  in  it  they  are,  by  contrast,  far  more 
impressive  than  the  general  darkness  of  the  inter- 
stellar expanse  seen  in  other  directions.  Yet  even 
that  expanse  is  not  everywhere  equally  dark,  for  it 
contains  gloomy  deeps  discernible  with  careful  watch- 
ing. Here,  too,  contrast  plays  an  important  part, 
though  less  striking  than  within  the  galactic  region. 
Some  of  Sir  William  Herschel's  observations  appear 
to  indicate  an  association  between  these  tenebrious 
spots  and  neighboring  star-clouds  and  nebulae.  It  is 
an  illuminating  bit  of  astronomical  history  that  when 
he  was  sweeping  the  then  virgin  heavens  with  his  great 
telescopes  he  was  accustomed  to  say  to  his  sister  who, 
note-book  in  hand,  waited  at  his  side  to  take  down 
his  words,  fresh  with  the  inspiration  of  discovery: 
"Prepare  to  write \  the  nebulae  are  coming;  here  space 
is  vacant." 

The  most  famous  of  the  "coal-sacks,"  and  the  first 


to  be  brought  to  general  attention  before  astronomers 
had  awakened  to  the  significance  of  such  things,  lies 
adjacent  to  the  "Southern  Cross,"  and  is  truly  an 
amazing  phenomenon.  It  is  not  alone  the  conspicu- 
ousness  of  this  celestial  vacancy,  opening  suddenly  in 
the  midst  of  one  of  the  richest  parts  of  the  Galaxy, 
that  has  given  it  its  fame,  but  quite  as  much  the  super- 
stitious awe  with  which  it  was  regarded  by  the  early 
explorers  of  the  South  Seas.  To  them,  as  well  as  to 
those  who  listened  in  wrapt  wonder  to  their  tales,  the 
"Coal-sack"  seemed  to  possess  some  occult  connection 
with  the  mystic  "Cross."  In  the  eyes  of  the  sailors 
it  was  not  a  vacancy  so  much  as  a  sable  reality  in  the 
sky,  and  as,  shuddering,  they  stared  at  it,  they  piously 
crossed  themselves.  It  was  another  of  the  magical 
wonders  of  the  unknown  South,  and  as  such  it  formed 
the  basis  of  many  a  "wild  surmise"  and  many  a  sea- 
dog's  yarn.  Scientific  investigation  has  not  diminished 
its  prestige,  and  to-day  no  traveller  in  the  southern 
hemisphere  is  indifferent  to  its  fascinating  strangeness, 
while  some  find  it  the  most  impressive  spectacle  of  the 
antarctic  heavens. 

All  around,  up  to  the  very  edge  of  the  yawning  gap, 
the  sheen  of  the  Milky  Way  is  surpassingly  glorious; 
but  there,  as  if  in  obedience  to  an  almighty  edict, 
everything  vanishes.  A  single  faint  star  is  visible 
within  the  opening,  producing  a  curious  effect  upon  the 
sensitive  spectator,  like  the  sight  of  a  tiny  islet  in  the 
midst  of  a  black,  motionless,  waveless  tarn.  The  di- 
mensions of  the  lagoon  of  darkness,  which  is  oval  or 
pear-shaped,  are  eight  degrees  by  five,  so  that  it  oc- 
cupies a  space  in  the  sky  about  one  hundred  and  thirty 



times  greater  than  the  area  of  the  full  moon.  It 
attracts  attention  as  soon  as  the  eye  is  directed  toward 
the  quarter  where  it  exists,  and  by  virtue  of  the  rarity 
of  such  phenomena  it  appears  a  far  greater  wonder 
than  the  drifts  of  stars  that  are  heaped  around  it. 
Now  that  observatories  are  multiplying  in  the  southern 
hemisphere,  the  great  austral  "  Coal  -sack"  will,  no 
doubt,  receive  attention  proportioned  to  its  importance 
as  one  of  the  most  significant  features  of  the  sky. 
Already  at  the  Sydney  Observatory  photographs  have 
shown  that  the  southern  portion  of  this  Dead  Sea  of 
Space  is  not  quite  ''bottomless,"  although  its  northern 
part  defies  the  longest  sounding  lines  of  the  astronomer. 

There  is  a  similar,  but  less  perfect,  "coal-sack"  in 
the  northern  hemisphere,  in  the  constellation  of 
"The  Swan,"  which,  strange  to  say,  also  contains  a 
well-marked  figure  of  a  cross  outlined  by  stars.  This 
gap  lies  near  the  top  of  the  cross-shaped  figure.  It  is 
best  seen  by  averted  vision,  which  brings  out  the  con- 
trast with  the  Milky  Way,  which  is  quite  brilliant 
around  it.  It  does  not,  however,  exercise  the  same 
weird  attraction  upon  the  eye  as  the  southern  "Coal- 
sack,"  for  instead  of  looking  like  an  absolute  void  in 
the  sky,  it  rather  appears  as  if  a  canopy  of  dark  gauze 
had  been  drawn  over  the  stars.  We  shall  see  the 
possible  significance  of  this  appearance  later. 

Just  above  the  southern  horizon  of  our  northern 
middle  latitudes,  in  summer,  where  the  Milky  Way 
breaks  up  into  vast  sheets  of  nebulous  luminosity, 
lying  over  and  between  the  constellations  Scorpio  and 
Sagittarius,  there  is  a  remarkable  assemblage  of 
"coal-sacks,"  though  none  is  of  great  size.  One  of 


THE    MILKY    WAY.       REGION    NEAR   M    8.       PHOTOGRAPHED    BY 


them,  near  a  conspicuous  star  -  cluster  in  Scorpio, 
80  M,  is  interesting  for  having  been  the  first  of  these 
strange  objects  noted  by  Herschel.  Probably  it  was 
its  nearness  to  80  M  which  suggested  to  his  mind  the 
apparent  connection  of  such  vacancies  with  star- 
clusters  which  we  have  already  mentioned. 

But  the  most  marvellous  of  the  "coal-sacks"  are 
those  that  have  been  found  by  photography  in 
Sagittarius.  One  of  Barnard's  earliest  and  most 
excellent  photographs  includes  two  of  them,  both  in 
the  star-cluster  8  M.  The  larger,  which  is  roughly 
rectangular  in  outline,  contains  one  little  star,  and  its 
smaller  neighbor  is  lune-shaped — surely  a  most  singu- 
lar form  for  such  an  object.  Both  are  associated  with 
curious  dark  lanes  running  through  the  clustered 
stars  like  trails  in  the  woods.  Along  the  borders  of 
these  lanes  the  stars  are  ranked  in  parallel  rows,  and 
what  may  be  called  the  bottoms  of  the  lanes  are  not 
entirely  dark,  but  pebbled  with  faint  stellar  points. 
One  of  them  which  skirts  the  two  dark  gaps  and 
traverses  the  cluster  along  its  greatest  diameter  is 
edged  with  lines  of  stars,  recalling  the  alignment  of  the 
trees  bordering  a  French  highway.  This  road  of  stars 
cannot  be  less  than  many  billions  of  miles  in  length! 

All  about  the  cluster  the  bed  of  the  Galaxy  is 
strangely  disturbed,  and  in  places  nearly  denuded, 
as  if  its  contents  had  been  raked  away  to  form  the 
immense  stack  and  the  smaller  accumulations  of 
stars  around  it.  The  well-known  "Trifid  Nebula" 
is  also  included  in  the  field  of  the  photograph,  which 
covers  a  truly  marvellous  region,  so  intricate  in  its 
mingling  of  nebulae,  star-clusters,  star-swarms,  star- 



streams,  and  dark  vacancies  that  no  description  can 
do  it  justice.  Yet,  chaotic  as  it  appears,  there  is  an 
unmistakable  suggestion  of  unity  about  it,  impressing 
the  beholder  with  the  idea  that  all  the  different  parts 
are  in  some  way  connected,  and  have  not  been  for- 
tuitously thrown  together.  Miss  Agnes  M.  Clerke 
made  the  striking  remark  that  the  dusky  lanes  in 
8  M  are  exemplified  on  the  largest  scale  in  the  great 
rift  dividing  the  Milky  Way,  from  Cygnus  in  the  north- 
ern hemisphere  all  the  way  to  the  "Cross"  in  the 
southern.  Similar  lanes  are  found  in  many  other 
clusters,  and  they  are  generally  associated  with  flank- 
ing rows  of  stars,  resembling  in  their  arrangement  the 
thick-set  houses  and  villas  along  the  roadways  that 
traverse  the  approaches  to  a  great  city. 

But  to  return  to  the  black  gaps.  Are  they  really 
windows  in  the  star- walls  of  the  universe  ?  Some  of 
them  look  rather  as  if  they  had  been  made  by  a  shell 
fired  through  a  luminous  target,  allowing  the  eye  to 
range  through  the  hole  into  void  space  beyond.  If 
science  is  discreetly  silent  about  these  things,  what 
can  the  more  venturesome  and  less  responsible  imag- 
ination suggest?  Would  a  huge  "runaway  sun,"  like 
Arcturus,  for  instance,  make  such  an  opening  if  it 
should  pass  like  a  projectile  through  the  Milky  Way  ? 
It  is  at  least  a  stimulating  inquiry.  Being  probably 
many  thousands  of  times  more  massive  than  the 
galactic  stars,  such  a  stellar  missile  would  not  be 
stopped  by  them,  though  its  direction  of  flight  might 
be  altered.  It  would  drag  the  small  stars  lying  close 
to  its  course  out  of  their  spheres,  but  the  ultimate 
tendency  of  its  attraction  would  be  to  sweep  them 



round  in  its  wake,  thus  producing  rather  a  star-swarm 
than  a  vacancy.  Those  that  were  very  close  to  it 
might  be  swept  away  in  its  rush  and  become  its  sat- 
ellites, careering  away  with  it  in  its  flight  into  outer 
space ;  but  those  that  were  farther  off,  and  they  would, 
of  course,  greatly  outnumber  the  near  ones,  would 
tend  inward  from  all  sides  toward  the  line  of  flight,' 
as  dust  and  leaves  collect  behind  a  speeding  motor 
(though  the  forces  operating  would  be  different) ,  and 
would  fill  up  the  hole,  if  hole  there  were.  A  swarm 
thus  collected  should  be  rounded  in  outline  and  bor- 
dered with  a  relatively  barren  ring  from  which  the 
stars  had  been  " sucked"  away.  In  a  general  sense 
the  8  M  cluster  answers  to  this  description,  but  even 
if  we  undertook  to  account  for  its  existence  by  a  sup- 
position like  the  above,  the  black  gaps  would  remain 
unexplained,  unless  one  could  make  a  further  draft 
on  the  imagination  and  suggest  that  the  stars  had  been 
thrown  into  a  vast  eddy,  or  system  of  eddies,  whose 
vortices  appear  as  dark  holes.  Only  a  maelstrom- 
like  motion  could  keep  such  a  funnel  open,  for  with- 
out regard  to  the  impulse  derived  from  the  projectile, 
the  proper  motions  of  the  stars  themselves  would 
tend  to  fill  it.  Perhaps  some  other  cause  of  the 
whirling  motion  may  be  found.  As  we  shall  see 
when  we  come  to  the  spiral  nebulae,  gyratory  move- 
ments are  exceedingly  prevalent  throughout  the 
universe,  and  the  structure  of  the  Milky  Way  is  every- 
where suggestive  of  them.  But  this  is  hazardous 
sport  even  for  the  imagination — to  play  with  suns  as 
if  they  were  but  thistle-down  in  the  wind  or  corks  in 
a  mill-race. 



Another  question  arises:  What  is  the  thickness  of 
the  hedge  of  stars  through  which  the  holes  penetrate  ? 
Is  the  depth  of  the  openings  proportionate  to  their 
width  ?  In  other  words,  is  the  Milky  Way  round  in 
section  like  a  rope,  or  flat  and  thin  like  a  ribbon? 
The  answer  is  not  obvious,  for  we  have  little  or  no 
information  concerning  the  relative  distances  of  the 
faint  galactic  stars.  It  would  be  easier,  certainly,  to 
conceive  of  openings  in  a  thin  belt  than  in  a  massive 
ring,  for  in  the  first  case  they  would  resemble  mere  rifts 
and  breaks,  while  in  the  second  they  would  be  like  wells 
or  bore-holes.  Then,  too,  the  fact  that  the  Milky  Way 
is  not  a  continuous  body  but  is  made  up  of  stars  whose 
actual  distances  apart  is  great,  offers  another  quan- 
dary; persistent  and  sharply  bordered  apertures  in 
such  an  assemblage  are  a  priori  as  improbable,  if  not 
impossible,  as  straight,  narrow  holes  running  through 
a  swarm  of  bees. 

The  difficulty  of  these  questions  indicates  one  of 
the  reasons  why  it  has  been  suggested  that  the  seem- 
ing gaps,  or  many  of  them,  are  not  openings  at  all, 
but  opaque  screens  cutting  off  the  light  from  stars 
behind  them.  That  this  is  quite  possible  in  some  cases 
is  shown  by  Barnard's  later  photographs,  particularly 
those  of  the  singular  region  around  the  star  Rho 
Ophiuchi.  Here  are  to  be  seen  sombre  lanes  and 
patches,  apparently  forming  a  connected  system 
which  covers  an  immense  space,  and  which  their  dis- 
coverer thinks  may  constitute  a  "dark  nebula."  This 
seems  at  first  a  startling  suggestion;  but,  after  all, 
why  should  there  not  be  dark  nebulae  as  well  as 
visible  ones?  In  truth,  it  has  troubled  some  as- 



tronomers  to  explain  the  luminosity  of  the  bright 
nebulae,  since  it  is  not  to  be  supposed  that  matter  in 
so  diffuse  a  state  can  be  incandescent  through  heat, 
and  phosphorescent  light  is  in  itself  a  mystery.  The 
supposition  is  also  in  accord  with  what  we  know  of 
the  existence  of  dark  solid  bodies  in  space.  Many 
bright  stars  are  accompanied  by  obscure  companions, 
sometimes  as  massive  as  themselves;  the  planets  are 
non-luminous;  the  same  is  true  of  meteors  before 
they  plunge  into  the  atmosphere  and  become  heated 
by  friction;  and  many  plausible  reasons  have  been 
found  for  believing  that  space  contains  as  many  ob- 
scure as  shining  bodies  of  great  size.  It  is  not  so 
difficult,  after  all,  then,  to  believe  that  there  are  im- 
mense collections  of  shadowy  gases, and  meteoric  dust 
whose  presence  is  only  manifested  when  they  inter- 
cept the  light  coming  from  shining  bodies  behind 

This  would  account  for  the  apparent  extinguish- 
ment of  light  in  open  space,  which  is  indicated  by  the 
falling  off  in  relative  number  of  telescopic  stars  below 
the  tenth  magnitude.  Even  as  things  are,  the  amount 
of  light  coming  to  us  from  stars  too  faint  to  be  seen 
with  the  naked  eye  is  so  great  that  the  statement  of 
it  generally  surprises  persons  who  are  unfamiliar 
with  the  inner  facts  of  astronomy.  It  has  been  cal- 
culated that  on  a  clear  night  the  total  starlight  from 
the  entire  celestial  sphere  amounts  to  one-sixtieth  of 
the  light  of  the  full  moon;  but  of  this  less  than  one- 
twenty-fifth  is  due  to  stars  separately  distinguished 
by  the  eye.  If  there  were  no  obscuring  medium  in 
space,  it  is  probable  that  the  amount  of  starlight 



would  be  noticeably  and  perhaps  enormously  in- 

But  while  it  seems  certain  that  some  of  the  obscure 
spots  in  the  Milky  Way  are  due  to  the  presence  of 
''dark  nebulae, "  or  concealing  veils  of  one  kind  or 
another,  it  is  equally  certain  that  there  are  many 
which  are  true  apertures,  however  they  may  have 
been  formed,  and  by  whatever  forces  they  may  be 
maintained.  These,  then,  are  veritable  windows  of 
the  Galaxy,  and  when  looking  out  of  them  one  is 
face  to  face  with  the  great  mystery  of  infinite  space. 
There  the  known  universe  visibly  ends,  but  mani- 
festly space  itself  does  not  end  there.  It  is  not  within 
the  power  of  thought  to  conceive  an  end  to  space, 
for  the  instant  we  think  of  a  terminal  point  or  line  the 
mind  leaps  forward  to  the  beyond.  There  must  be 
space  outside  as  well  as  inside.  Eternity  of  time  and 
infinity  of  space  are  ideas  that  the  intellect  cannot 
fully  grasp,  but  neither  can  it  grasp  the  idea  of  a 
limitation  to  either  space  or  time.  The  metaphysical 
conceptions  of  hypergeometry,  or  fourth-dimensional 
space,  do  not  aid  us. 

Having,  then,  discovered  that  the  universe  is  a  thing 
contained  in  something  indefinitely  greater  than  itself ; 
having  looked  out  of  its  windows  and  found  only  the 
gloom  of  starless  night  outside — what  conclusions  are 
we  to  draw  concerning  the  beyond?  It  seems  as 
empty  as  a  vacuum,  but  is  it  really  so  ?  If  it  be,  then 
our  universe  is  a  single  atom  astray  in  the  infinite; 
it  is  the  only  island  in  an  ocean  without  shores;  it 
is  the  one  oasis  in  an  illimitable  desert.  Then  the 
Milky  Way,  with  its  wide-flung  garland  of  stars,  is 



afloat  like  a  tiny  smoke-wreath  amid  a  horror  of 
immeasurable  vacancy,  or  it  is  an  evanescent  and 
solitary  ring  of  sparkling  froth  cast  up  for  a  moment 
on  the  viewless  billows  of  immensity.  From  such 
conclusions  the  mind  instinctively  shrinks.  It  pre- 
fers to  think  that  there  is  something  beyond,  though 
we  cannot  see  it.  Even  the  universe  could  not  bear 
to  be  alone — a  Crusoe  lost  in  the  Cosmos!  As  the 
inhabitants  of  the  most  elegant  chateau,  with  its 
gardens,  parks,  and  crowds  of  attendants,  would  die 
of  loneliness  if  they  did  not  know  that  they  have 
neighbors,  though  not  seen,  and  that  a  living  world 
of  indefinite  extent  surrounds  them,  so  we,  when  we 
perceive  that  the  universe  has  limits,  wish  to  feel  that 
it  is  not  solitary;  that  beyond  the  hedges  and  the 
hills  there  are  other  centres  of  life  and  activity. 
Could  anything  be  more  terrible  than  the  thought  of 
an  isolated  universe?  The  greater  the  being,  the 
greater  the  aversion  to  seclusion.  Only  the  infinite 
satisfies ;  in  that  alone  the  mind  finds  rest. 

We  are  driven,  then,  to  believe  that  the  universal 
night  which  envelops  us  is  not  tenantlessi  that  as 
we  stare  out  of  the  star-framed  windows  of  the 
Galaxy  and  see  nothing  but  uniform  blackness,  the 
fault  is  with  our  eyes  or  is  due  to  an  obscuring  me- 
dium. Since  our  universe  is  limited  in  extent,  there 
must  be  other  universes  beyond  it  on  all  sides.  Per- 
haps if  we  could  carry  our  telescopes  to  the  verge  of 
the  great  " Coal-sack"  near  the  "Cross,"  being  then 
on  the  frontier  of  our  starry  system,  we  could  discern, 
sparkling  afar  off  in  the  vast  night,  some  of  the  outer 
galaxies.  They  may  be  grander  than  ours,  just  as 



many  of  the  suns  surrounding  us  are  immensely 
greater  than  ours.  If  we  could  take  our  stand  some- 
where in  the  midst  of  immensity  and,  with  vision  of 
infinite  reach,  look  about  us,  we  should  perhaps  see  a 
countless  number  of  stellar  systems,  amid  which  ours 
would  be  unnoticeable,  like  a  single  star  among  the 
multitude  glittering  in  the  terrestrial  sky  on  a  clear 
night.  Some  might  be  in  the  form  of  a  wreath,  like 
our  own;  some  might  be  globular,  like  the  great  star- 
clusters  in  Hercules  and  Centaurus;  some  might  be 
glittering  circles,  or  disks,  or  rings  within  rings.  If 
we  could  enter  them  we  should  probably  find  a  vast 
variety  of  composition,  including  elements  unknown 
to  terrestrial  chemistry ;  for  while  the  visible  universe 
appears  to  contain  few  if  any  substances  not  existing 
on  the  earth  or  in  the  sun,  we  have  no  warrant  to 
assume  that  others  may  not  exist  in  infinite  space. 

And  how  as  to  gravitation?  We  do  not  know  that 
gravitation  acts  beyond  the  visible  universe,  but  it 
is  reasonable  to  suppose  that  it  does.  At  any  rate, 
if  we  let  go  its  sustaining  hand  we  are  lost,  and  can  only 
wander  hopelessly  in  our  speculations,  like  children 
astray.  If  the  empire  of  gravitation  is  infinite,  then 
the  various  outer  systems  must  have  some,  though 
measured  by  our  standards  an  imperceptible,  attrac- 
tive influence  upon  each  other,  for  gravitation  never 
lets  go  its  hold,  however  great  the  space  over  which  it 
is  required  to  act.  Just  as  the  stars  about  us  are  all 
in  motion,  so  the  starry  systems  beyond  our  sight 
may  be  in  motion,  and  our  system  as  a  whole  may 
be  moving  in  concert  with  them.  If  this  be  so,  then 
after  interminable  ages  the  aspect  of  the  entire  system 



of  systems  must  change,  its  various  members  assuming 
new  positions  with  respect  to  one  another.  In  the 
course  of  time  we  may  even  suppose  that  our  universe 
will  approach  relatively  close  to  one  of  the  others; 
and  then,  if  men  are  yet  living  on  the  earth,  they  may 
glimpse  through  the  openings  which  reveal  nothing 
to  us  now,  the  lights  of  another  nearing  star  system, 
like  the  signals  of  a  strange  squadron,  bringing  them 
the  assurance  (which  can  be  but  an  inference  at 
present)  that  the  ocean  of  space  has  other  argosies 
venturing  on  its  limitless  expanse. 

There  remains  the  question  of  the  luminiferous  \ 
ether  by  whose  agency  the  waves  of  light  are  borne 
through  space.  The  ether  is  as  mysterious  as  gravita- 
tion. With  regard  to  either  we  only  infer  its  exist- 
ence from  the  effects  which  we  ascribe  to  it.  Evident- 
ly the  ether  must  extend  as  far  as  the  most  distant 
visible  stars.  But  does  it  continue  on  indefinitely  in 
outer  space?  If  it  does,  then  the  invisibility  of  the 
other  systems  must  be  due  to  their  distance  diminish- 
ing the  quantity  of  light  that  comes  from  them  below 
the  limit  of  perceptibility,  or  to  the  interposition  of 
absorbing  media;  if  it  does  not,  then  the  reason  why 
we  cannot  see  them  is  owing  to  the  absence  of  a 
means  of  conveyance  for  the  light- waves,  as  the  lack 
of  an  interplanetary  atmosphere  prevents  us  from 
hearing  the  thunder  of  sun-spots.  (It  is  interesting 
to  recall  that  Mr.  Edison  was  once  credited  with  the 
intention  to  construct  a  gigantic  microphone  which 
should  render  the  roar  of  sun-spots  audible  by  trans- 
forming the  electric  vibrations  into  sound-waves.) 
On  this  supposition  each  starry  system  would  be  en- 


veloped  in  its  own  globule  of  ether,  and  no  light  could 
cross  from  one  to  another.  But  the  probability  is 
that  both  the  ether  and  gravitation  are  ubiquitous, 
and  that  all  the  stellar  systems  are  immersed  in  the 
former  like  clouds  of  phosphorescent  organisms  in 
the  sea. 

So  astronomy  carries  the  mind  from  height  to 
greater  height.  Men  were  long  in  accepting  the 
proofs  of  the  relative  insignificance  of  the  earth; 
they  were  more  quickly  convinced  of  the  comparative 
littleness  of  the  solar  system;  and  now  the  evidence 
assails  their  reason  that  what  they  had  regarded  as 
the  universe  is  only  one  mote  gleaming  in  the  sun- 
beams of  Infinity. 



IN  the  preceding  chapter  we  have  seen  something 
of    the    strangely   complicated    structure   of    the 
Galaxy,  or  Milky  Way.     We  now  proceed  to  study 
more  comprehensively  that  garlanded  "  Pathway  of 
the  Gods." 

Judged  by  the  eye  alone,  the  Milky  Way  is  one  of 
the  most  delicately  beautiful  phenomena  in  the  entire 
realm  of  nature — a  shimmer  of  silvery  gauze  stretched 
across  the  sky ;  but  studied  in  the  light  of  its  revela- 
tions, it  is  the  most  stupendous  object  presented  to 
human  ken.  Let  us  consider,  first,  its  appearance  to 
ordinary  vision.  Its  apparent  position  in  the  sky 
shifts  according  to  the  season.  On  a  serene,  cloudless 
summer  evening,  in  the  absence  of  the  moon,  whose 
light  obscures  it,  one  sees  the  Galaxy  spanning  the 
heavens  from  north  to  southeast  of  the  zenith  like  a 
phosphorescent  arch.  In  early  spring  it  forms  a 
similar  but,  upon  the  whole,  less  brilliant  arch  west  of 
the  zenith.  Between  spring  and  summer  it  lies  like 
a  long,  faint  twilight  band  along  the  northern  horizon. 
At  the  beginning  of  winter  it  again  forms  an  arch, 
this  time  spanning  the  sky  from  east  to  west,  a  little 
north  of  the  zenith.  These  are  its  positions  as 



viewed  from  the  mean  latitude  of  the  United  States. 
Even  the  beginner  in  star-gazing  does  not  have  to 
watch  it  throughout  the  year  in  order  to  be  convinced 
that  it  is,  in  reality,  a  great  circle,  extending  entirely 
around  the  celestial  sphere.  We  appear  to  be  situ- 
ated near  its  centre,  but  its  periphery  is  evidently  far 
away  in  the  depths  of  space. 

Although  to  the  casual  observer  it  seems  but  a 
delicate  scarf  of  light,  brighter  in  some  places  than  in 
others,  but  hazy  and  indefinite  at  the  best,  such  is 
not  its  appearance  to  those  who  study  it  with  care. 
They  perceive  that  it  is  an  organic  whole,  though 
marvellously  complex  in  detail.  The  telescope  shows 
that  it  consists  of  stars  too  faint  and  small  through 
excess  of  distance  to  be  separately  visible.  Of  the 
hundred  million  suns  which  some  estimates  have  fixed 
as  the  probable  population  of  the  starry  universe, 
the  vast  majority  (at  least  thirty  to  one)  are  included 
in  this  strange  belt  of  misty  light.  But  they  are  not 
uniformly  distributed  in  it;  on  the  contrary,  they 
are  arrayed  in  clusters,  knots,  bunches,  clouds,  and 
streams.  The  appearance  is  somewhat  as  if  the 
Galaxy  consisted  of  innumerable  swarms  of  silver- 
winged  bees,  more  or  less  intermixed,  some  massed 
together,  some  crossing  the  paths  of  others,  but  all 
governed  by  a  single  purpose  which  leads  them  to 
encircle  the  region  of  space  in  which  we  are  situ- 

From  the  beginning  of  the  systematic  study  of  the 
heavens,  the  fact  has  been  recognized  that  the  form 
of  the  Milky  Way  denotes  the  scheme  of  the  sidereal 
system.  At  first  it  was  thought  that  the  shape  of  the 



system  was  that  of  a  vast  round  disk,  flat  like  a  cheese, 
and  filled  with  stars,  our  sun  and  his  relatively  few 
neighbors  being  placed  near  the  centre.  According 
to  this  view,  the  galactic  belt  was  an  effect  of  per- 
spective ;  for  when  looking  in  the  direction  of  the  plane 
of  the  disk,  the  eye  ranged  through  an  immense  ex- 
tension of  stars  which  blended  into  a  glimmering  blur, 
surrounding  us  like  a  ring;  while  when  looking  out 
from  the  sides  of  the  disk  we  saw  but  few  stars,  and  in 
those  directions  the  heavens  appeared  relatively 
blank.  Finally  it  was  recognized  that  this  theory 
did  not  correspond  with  the  observed  appearances, 
and  it  became  evident  that  the  Milky  Way  was  not 
a  mere  effect  of  perspective,  but  an  actual  band  of 
enormously  distant  stars,  forming  a  circle  about  the 
sphere,  the  central  opening  of  the  ring  (containing 
many  scattered  stars)  being  many  times  broader  than 
the  width  of  the  ring  itself.  Our  sun  is  one  of  the 
scattered  stars  in  the  central  opening. 

As  already  remarked,  the  ring  of  the  Galaxy  is  very 
irregular,  and  in  places  it  is  partly  broken.  With 
its  sinuous  outline,  its  pendant  sprays,  its  graceful 
and  accordant  curves,  its  bunching  of  masses,  its 
occasional  interstices,  and  the  manifest  order  of  a 
general  plan  governing  the  jumble  of  its  details,  it 
bears  a  remarkable  resemblance  to  a  garland — a  fact 
which  appears  the  more  wonderful  when  we  recall  its 
composition.  That  an  elm -tree  should  trace  the 
lines  of  beauty  with  its  leafy  and  pendulous  branches 
does  not  surprise  us;  but  we  can  only  gaze  with 
growing  amazement  when  we  behold  a  hundred 
million  suns  imitating  the  form  of  a  chaplet!  And 


then  we  have  to  remember  that  this  form  furnishes 
the  ground-plan  of  the  universe. 

As  an  indication  of  the  extraordinary  speculations 
to  which  the  mystery  of  the  Milky  Way  has  given  rise, 
a  theory  recently  (1909)  proposed  by  Prof.  George  C. 
Comstock  may  be  mentioned.  Starting  with  the 
data  (first)  that  the  number  of  stars  increases  as 
the  Milky  Way  is  approached,  and  reaches  a  maxi- 
mum in  its  plane,  while  on  the  other  hand  the  number 
of  nebulae  is  greatest  outside  the  Milky  Way  and  in- 
creases with  distance  from  it,  and  (second)  that  the 
Milky  Way,  although  a  complete  ring,  is  broad  and 
diffuse  on  one  side  through  one-half  its  course — that 
half  alone  containing  nebulae — and  relatively  narrow 
and  well  defined  on  the  opposite  side,  the  author 
of  this  singular  speculation  avers  that  these  facts  can 
best  be  explained  by  supposing  that  the  invisible 
universe  consists  of  two  interpenetrating  parts,  one 
of  which  is  a  chaos  of  indefinite  extent,  strewn  with 
stars  and  nebulous  dust,  and  the  other  a  long,  broad 
but  comparatively  thin  cluster  of  stars,  including  the 
sun  as  one  of  its  central  members.  This  flat  star- 
cluster  is  conceived  to  be  moving  edgewise  through 
the  chaos,  and,  according  to  Professor  Comstock,  it 
acts  after  the  manner  of  a  snow-plough  sweeping  away 
the  cosmic  dust  and  piling  it  on  either  hand  above  and 
below  the  plane  of  the  moving  cluster.  It  thus  forms 
a  transparent  rift,  through  which  we  see  farther  and 
command  a  view  of  more  stars  than  through  the  in- 
tensified dust-clouds  on  either  hand.  This  rift  is  the 
Milky  Way.  The  dust  thrown  aside  toward  the  poles 
of  the  Milky  Way  is  the  substance  of  the  nebulae 



which  abound  there.  Ahead,  where  the  front  of  the 
star-plough  is  clearing  the  way,  the  chaos  is  nearer 
at  hand,  and  consequently  there  the  rift  subtends  a 
broader  angle,  and  is  filled  with  primordial  dust, 
which,  having  been  annexed  by  the  vanguard  of  the 
star-swarm,  forms  the  nebulae  seen  only  in  that  part 
of  the  Milky  Way.  But  behind,  the  rift  appears 
narrow  because  there  we  look  farther  away  between 
dust-clouds  produced  ages  ago  by  the  front  of  the 
plough,  and  no  scattered  dust  remains  in  that  part  of 
the  rift. 

In  quoting  an  outline  of  this  strikingly  original 
theory  the  present  writer  should  not  be  understood 
as  assenting  to  it.  That  it  appears  bizarre  is  not,  in 
itself,  a  reason  for  rejecting  it,  when  we  are  dealing 
with  so  problematical  and  enigmatical  a  subject  as  the 
Milky  Way;  but  the  serious  objection  is  that  the 
theory  does  not  sufficiently  accord  with  the  observed 
phenomena.  There  is  too  much  evidence  that  the 
Milky  Way  is  an  organic  system,  however  fantastic 
its  form,  to  permit  the  belief  that  it  can  only  be  a 
rift  in  chaotic  clouds.  As  with  every  organism,  we 
find  that  its  parts  are  more  or  less  clearly  repeated 
in  its  ensemble.  Among  all  the  strange  things  that 
the  Milky  Way  contains  there  is  nothing  so  extraor- 
dinary as  itself.  Every  astronomer  must  many 
times  have  found  himself  marvelling  at  it  in  those 
comparatively  rare  nights  when  it  shows  all  its 
beauty  and  all  its  strangeness.  In  its  great  broken 
rifts,  divisions,  and  spirals  are  found  the  gigantic 
prototypes  of  similar  forms  in  its  star-clouds  and 
clusters.  As  we  have  said,  it  determines  the  general 


shape  of  the  whole  sidereal  system.  Some  of  the 
brightest  stars  in  the  sky  appear  to  hang  like  jewels 
suspended  at  the  ends  of  tassels  dropped  from  the 
Galaxy.  Among  these  pendants  are  the  Pleiades 
and  the  Hyades.  Orion,  too,  the  "Mighty  Hunter," 
is  caught  in  "a  loop  of  light"  thrown  out  from  it. 
The  majority  of  the  great  first-magnitude  stars  seem 
related  to  it,  as  if  they  formed  an  inner  ring  inclined 
at  an  angle  of  some  twenty  degrees  to  its  plane. 
Many  of  the  long  curves  that  set  off  from  it  on  both 
sides  are  accompanied  by  corresponding  curves  of 
lucid  stars.  In  a  word,  it  offers  every  appearance 
of  structural  connection  with  the  entire  starry  system. 
That  the  universe  should  have  assumed  the  form  of 
a  wreath  is  certainly  a  matter  for  astonishment ;  but 
it  would  have  been  still  more  astonishing  if  it  had 
been  a  cube,  a  rhomboid,  or  a  dodecahedron,  for 
then  we  should  have  had  to  suppose  that  something 
resembling  the  forces  that  shape  crystals  had  acted 
upon  the  stars,  and  the  difficulty  of  explaining  the 
universe  by  the  law  of  gravitation  would  have  been 

From  the  Milky  Way  as  a  whole  we  pass  to  the  vast 
clouds,  swarms,  and  clusters  of  stars  of  which  it  is 
made  up.  It  may  be,  as  some  astronomers  hold, 
that  most  of  the  galactic  stars  are  much  smaller  than 
the  sun,  so  that  their  faintness  is  not  due  entirely  to 
the  effect  of  distance.  Still,  their  intrinsic  brilliance 
attests  their  solar  character,  and  considering  their 
remoteness,  which  has  been  estimated  at  not  less  than 
ten  thousand  to  twenty  thousand  light-years  (a  light- 
year  is  equal  to  nearly  six  thousand  million  miles) 



their  actual  masses  cannot  be  extremely  small.  The 
minutest  of  them  are  entitled  to  be  regarded  as  real 
suns,  and  they  vary  enormously  in  magnitude.  The 
effects  of  their  attractions  upon  one  another  can  only 
be  inferred  from  their  clustering,  because  their 
relative  movements  are  not  apparent  on  account  of 
the  brevity  of  the  observations  that  we  can  make. 
But  imagine  a  being  for  whom  a  million  years  would 
be  but  as  a  flitting  moment;  to  him  the  Milky  Way 
would  appear  in  a  state  of  ceaseless  agitation — swirl- 
ing with  "a  fury  of  whirlpool  motion." 

The  cloud-like  aspect  of  large  parts  of  the  Galaxy 
must  always  have  attracted  attention,  even  from 
naked-eye  observers,  but  the  true  star-clouds  were 
first  satisfactorily  represented  in  Barnard's  photo- 
graphs. The  resemblance  to  actual  clouds  is  often 
startling.  Some  are  close-packed  and  dense,  like 
cumuli;  some  are  wispy  or  mottled,  like  cirri.  The 
rifts  and  modulations,  as  well  as  the  general  outlines, 
are  the  same  as  those  of  clouds  of  vapor  or  dust,  and 
one  notices  also  the  characteristic  thinning  out  at  the 
edges.  But  we  must  beware  of  supposing  that  the 
component  suns  are  thickly  crowded  as  the  particles 
forming  an  ordinary  cloud.  They  look,  indeed,  as  if 
they  were  matted  together,  because  of  the  irradiation 
of  light,  but  in  reality  millions  and  billions  of  miles 
separate  each  star  from  its  neighbors.  Nevertheless 
they  form  real  assemblages,  whose  members  are  far 
more  closely  related  to  one  another  than  is  our  sun 
to  the  stars  around  him,  and  if  we  were  in  the  Milky 
Way  the  aspect  of  the  nocturnal  sky  would  be  mar- 
vellously different  from  its  present  appearance. 


Stellar  clouds  are  characteristic  of  the  Galaxy  and 
are  not  found  beyond  its  borders,  except  in  the 
"Magellanic  Clouds"  of  the  southern  hemisphere, 
which  resemble  detached  portions  of  the  Milky  Way. 
These  singular  objects  form  as  striking  a  peculiarity  of 
the  austral  heavens  as  does  the  great  "Coal -sack" 
described  in  Chapter  I.  But  it  is  their  isolation  that 
makes  them  so  remarkable,  for  their  composition  is 
essentially  galactic,  and  if  they  were  included  within 
its  boundaries  they  would  not  appear  more  wonderful 
than  many  other  parts  of  the  Milky  Way.  Placed 
where  they  are,  they  look  like  masses  fallen  from  the 
great  stellar  arch.  They  are  full  of  nebulae  and  star- 
clusters,  and  show  striking  evidences  of  spiral  move- 

Star-swarms,  which  are  also  characteristic  features 
of  the  Galaxy,  differ  from  star-clouds  very  much  in 
the  way  that  their  name  would  imply — i.e.,  their 
component  stars  are  so  arranged,  even  when  they  are 
countless  in  number,  that  the  idea  of  an  exceedingly 
numerous  assemblage  rather  than  that  of  a  cloud  is 
impressed  on  the  observer's  mind.  In  a  star-swarm 
the  separate  members  are  distinguishable  because 
they  are  either  larger  or  nearer  than  the  stars  com- 
posing a  "cloud."  A  splendid  example  of  a  true 
star-swarm  is  furnished  by  Chi  Persei,  in  that  part  of 
the  Milky  Way  which  runs  between  the  constella- 
tions Perseus  and  Cassiopeia.  This  swarm  is  much 
coarser  than  many  others,  and  can  be  seen  by  the 
naked  eye.  In  a  small  telescope  it  appears  double, 
as  if  the  suns  composing  it  had  divided  into  two 
parties  which  keep  on  their  way  side  by  side,  with 



some  commingling  of  their  members  where  the  skirts 
of  the  two  companies  come  in  contact. 

Smaller  than  either  star-clouds  or  star-swarms,  and 
differing  from  both  in  their  organization,  are  star- 
clusters.  These,  unlike  the  others,  are  found  outside 
as  well  as  inside  the  Milky  Way,  although  they  are 
more  numerous  inside  its  boundaries  than  elsewhere. 
The  term  star-cluster  is  sometimes  applied,  though 
improperly,  to  assemblages  which  are  rather  groups, 
such,  for  instance,  as  the  Pleiades.  In  their  most 
characteristic  aspect  star-clusters  are  of  a  globular 
shape — globes  of  suns!  A  famous  example  of  a 
globular  star-cluster,  but  one  not  included  in  the 
Milky  Way,  is  the  " Great  Cluster  in  Hercules." 
This  is  barely  visible  to  the  naked  eye,  but  a  small 
telescope  shows  its  character,  and  in  a  large  one  it 
presents  a  marvellous  spectacle.  Photographs  of 
such  clusters  are,  perhaps,  less  effective  than  those  of 
star-clouds,  because  the  central  condensation  of  stars 
in  them  is  so  great  that  their  light  becomes  blended 
in  an  indistinguishable  blur.  The  beautiful  effect  of 
the  incessant  play  of  infinitesimal  rays  over  the 
apparently  compact  surface  of  the  cluster,  as  if  it 
were  a  globe  of  the  finest  frosted  silver  shining  in  an 
electric  beam,  is  also  lost  in  a  photograph.  Still, 
even  to  the  eye  looking  directly  at  the  cluster  through 
a  powerful  telescope,  the  central  part  of  the  wonderful 
congregation  seems  almost  a  solid  mass  in  which  the 
stars  are  packed  like  the  ice  crystals  in  a  snowball. 

The  same  question  rises  to  the  lips  of  every  ob- 
server: How  can  they  possibly  have  been  brought 
into  such  a  situation?  The  marvel  does  not  grow 


less  when  we  know  that,  instead  of  being  closely  com- 
pacted, the  stars  of  the  cluster  are  probably  separated 
by  millions  of  miles;  for  we  know  that  their  distances 
apart  are  slight  as  compared  with  their  remoteness 
from  the  earth.  Sir  William  Herschel  estimated 
their  number  to  be  about  fourteen  thousand,  but  in 
fact  they  are  uncountable.  If  we  could  view  them 
from  a  point  just  within  the  edge  of  the  assemblage, 
they  would  offer  the  appearance  of  a  hollow  hemi- 
sphere emblazoned  with  stars  of  astonishing  brill- 
iancy; the  near-by  ones  unparalleled  in  splendor  by 
any  celestial  object  known  to  us,  while  the  more  dis- 
tant ones  would  resemble  ordinary  stars.  An  in- 
habitant of  the  cluster  would  not  know,  except  by  a 
process  of  ratiocination,  that  he  was  dwelling  in  a 
globular  assemblage  of  suns;  only  from  a  point  far 
outside  would  their  spherical  arrangement  become 
evident  to  the  eye.  Imagine  fourteen  thousand  fire- 
balloons  arranged  with  an  approach  to  regularity  in 
a  spherical  space — say,  ten  miles  in  diameter;  there 
would  be  an  average  of  less  than  thirty  in  every 
cubic  mile,  and  it  would  be  necessary  to  go  to  a  con- 
siderable distance  in  order  to  see  them  as  a  globular 
aggregation ;  yet  from  a  point  sufficiently  far  away 
they  would  blend  into  a  glowing  ball. 

Photographs  show  even  better  than  the  best  tele- 
scopic views  that  the  great  cluster  is  surrounded  with 
a  multitude  of  dispersed  stars,  suggestively  arrayed 
in  more  or  less  curving  lines,  which  radiate  from  the 
principal  mass,  with  which  their  connection  is  mani- 
fest. These  stars,  situated  outside  the  central  sphere, 
look  somewhat  like  vagrant  bees  buzzing  round  a  dense 

(Photographed  with  a  two- foot  reflector) 


swarm  where  the  queen  bee  is  settling.  Yet  while 
there  is  so  much  to  suggest  the  operation  of  central 
forces,  bringing  and  keeping  the  members  of  the 
cluster  together,  the  attentive  observer  is  also  im- 
pressed with  the  idea  that  the  whole  wonderful 
phenomenon  may  be  ike  result  of  explosion.  As  soon 
as  this  thought  seizes  the  mind,  confirmation  of  it 
seems  to  be  found  in  the  appearance  of  the  outlying 
stars,  which  could  be  as  readily  explained  by  the 
supposition  that  they  have  been  blown  apart  as  that 
they  have  flocked  together  toward  a  centre.  The 
probable  fact  that  the  stars  constituting  the  cluster 
are  very  much  smaller  than  our  sun  might  be  regarded 
as  favoring  the  hypothesis  of  an  explosion.  Of  their 
real  size  we  know  nothing,  but,  on  the  basis  of  an 
uncertain  estimate  of  their  parallax,  it  has  been  cal- 
culated that  they  may  average  forty-five  thousand 
miles  in  diameter — something  more  than  half  the 
diameter  of  the  planet  Jupiter.  Assuming  the  same 
mean  density,  fourteen  thousand  such  stars  might 
have  been  formed  by  the  explosion  of  a  body  about 
twice  the  size  of  the  sun.  This  recalls  the  theory 
of  Olbers,  which  has  never  been  altogether  abandoned 
or  disproved,  that  the  Asteroids  were  formed  by  the 
explosion  of  a  planet  circulating  between  the  orbits 
of  Mars  and  Jupiter.  The  Asteroids,  whatever  their 
manner  of  origin,  form  a  ring  around  the  sun;  but, 
of  course,  the  explosion  of  a  great  independent  body, 
not  originally  revolving  about  a  superior  centre  of 
gravitative  force,  would  not  result  in  the  formation 
of  a  ring  of  small  bodies,  but  rather  of  a  dispersed 
mass  of  them.  But  back  of  any  speculation  of  this 



kind  lies  the  problem,  at  present  insoluble:  How 
could  the  explosion  be  produced  ?  (See  the  question 
of  explosions  in  Chapters  VI  and  XIV.) 

Then,  on  the  other  hand,  we  have  the  observation 
of  Herschel,  since  abundantly  confirmed,  that  space 
is  unusually  vacant  in  the  immediate  neighborhood  of 
condensed  star-clusters  and  nebulae,  which,  as  far  as 
it  goes,  might  be  taken  as  an  indication  that  the 
assembled  stars  had  been  drawn  together  by  their 
mutual  attractions,  and  that  the  tendency  to  aggre- 
gation is  still  bringing  new  members  toward  the 
cluster.  But  in  that  case  there  must  have  been 
an  original  condensation  of  stars  at  that  point  in 
space.  This  could  probably  have  been  produced  by 
the  coagulation  of  a  great  nebula  into  stellar  nuclei, 
a  process  which  seems  now  to  be  taking  place  in  the 
Orion  Nebula. 

A  yet  more  remarkable  globular  star-cluster  exists 
in  the  southern  hemisphere,  Omega  Centauri.  In 
this  case  the  central  condensation  of  stars  presents 
an  almost  uniform  blaze  of  light.  Like  the  Hercules 
cluster,  that  in  Centaurus  is  surrounded  with  stars 
scattered  over  a  broad  field  and  showing  an  appear- 
ance of  radial  arrangement.  In  fact,  except  for  its 
greater  richness,  Omega  Centauri  is  an  exact  duplicate 
of  its  northern  rival.  Each  appears  to  an  imaginative 
spectator  as  a  veritable  ''city  of  suns."  Mathe- 
matics shrinks  from  the  task  of  disentangling  the 
maze  of  motions  in  such  an  assemblage.  It  would  seem 
that  the  chance  of  collisions  is  not  to  be  neglected, 
and  this  idea  finds  a  certain  degree  of  confirmation 
in  the  appearance  of  " temporary  stars"  which  have 




more  than  once  blazed  out  in,  or  close  by,  globular 

This  leads  up  to  the  notable  fact,  first  established 
by  Professor  Bailey  a  few  years  ago,  that  such  clusters 
are  populous  with  variable  stars.  Omega  Centauri 
and  the  Hercules  cluster  are  especially  remarkable  in 
this  respect.  The  variables  found  in  them  are  all 
of  short  period  and  the  changes  of  light  show  a  note- 
worthy tendency  to  uniformity.  The  first  thought 
is  that  these  phenomena  must  be  due  to  collisions 
among  the  crowded  stars,  but,  if  so,  the  encounters 
cannot  be  between  the  stars  themselves,  but  probably 
between  stars  and  meteor  swarms  revolving  around 
them.  Such  periodic  collisions  might  go  on  for  ages 
without  the  meteors  being  exhausted  by  incorpora- 
tion with  the  stars.  This  explanation  appears  all 
the  more  probable  because  one  would  naturally  ex- 
pect that  flocks  of  meteors  would  abound  in  a  close 
aggregation  of  stars.  It  is  also  consistent  with 
Perrine's  discovery — that  the  globular  star-clusters 
are  powdered  with  minute  stars  strewn  thickly  among 
the  brighter  ones. 

In  speaking  of  Professor  Comstock's  extraordinary 
theory  of  the  Milky  Way,  the  fact  was  mentioned  that, 
broadly  speaking,  the  nebulas  are  less  numerous  in 
the  galactic  belt  than  in  the  comparatively  open 
spaces  on  either  side  of  it,  but  that  they  are,  neverthe- 
less, abundant  in  the  broader  half  of  the  Milky  Way 
which  he  designates  as  the  front  of  the  gigantic 
"plough"  supposed  to  be  forcing  its  way  through 
the  enveloping  chaos.  In  and  around  the  Sagit- 
tarius region  the  intermingling  of  nebulae  and 



galactic  star  clouds  and  clusters  is  particularly  re- 
markable. That  there  is  a  causal  connection  no 
thoughtful  observer  can  doubt.  We  are  unable  to 
get  away  from  the  evidence  that  a  nebula  is  like  a 
seed-ground  from  which  stars  spring  forth;  or  we 
may  say  that  nebulas  resemble  clouds  in  whose 
bosom  raindrops  are  forming.  The  wonderful  as- 
pect of  the  admixtures  of  nebulae  and  star-clusters 
in  Sagittarius  has  been  described  in  Chapter  I.  We 
now  come  to  a  still  more  extraordinary  phenomenon 
of  this  kind — the  Pleiades  nebulas. 

The  group  of  the  Pleiades,  although  lying  outside 
the  main  course  of  the  Galaxy,  is  connected  with  it 
by  a  faint  loop,  and  is  the  scene  of  the  most  remark- 
able association  of  stars  and  nebulous  matter  known 
in  the  visible  universe.  The  naked  eye  is  unaware 
of  the  existence  of  nebulas  in  the  Pleiades,  or,  at  the 
best,  merely  suspects  that  there  is  something  of  the 
kind  there;  and  even  the  most  powerful  telescopes 
are  far  from  revealing  the  full  wonder  of  the  spectacle ; 
but  in  photographs  which  have  been  exposed  for 
many  hours  consecutively,  in  order  to  accumulate  the 
impression  of  the  actinic  rays,  the  revelation  is  stun- 
ning. The  principal  stars  are  seen  surrounded  by, 
and,  as  it  were,  drowned  in,  dense  nebulous  clouds  of 
an  unparalleled  kind.  The  forms  assumed  by  these 
clouds  seem  at  first  sight  inexplicable.  They  look 
like  fleeces,  or  perhaps  more  like  splashes  and  daubs 
of  luminous  paint  dashed  carelessly  from  a  brush. 
But  closer  inspection  shows  that  they  are,  to  a  large 
extent,  woven  out  of  innumerable  threads  of  filmy 
texture,  and  there  are  many  indications  of  spiral 



tendencies.  Each  of  the  bright  stars  of  the  group — 
Alcyone,  Merope,  Maia,  Electra,  Taygeta,  Atlas — is 
the  focus  of  a  dense  fog  (totally  invisible,  remember, 
alike  to  the  naked  eye  and  to  the  telescope),  and  these 
particular  stars  are  veiled  from  sight  behind  the 
strange  mists.  Running  in  all  directions  across  the 
relatively  open  spaces  are  nebulous  wisps  and  streaks 
of  the  most  curious  forms.  On  some  of  the  nebular 
lines,  which  are  either  straight  throughout,  or  if  they 
change  direction  do  so  at  an  angle,  little  stars  are 
strung  like  beads.  In  one  case  seven  or  eight  stars 
are  thus  aligned,  and,  as  if  to  emphasize  their  depend- 
ence upon  the  chain  which  connects  them,  when  it 
makes  a  slight  bend  the  file  of  stars  turns  the  same 
way.  Many  other  star  rows  in  the  group  suggest  by 
their  arrangement  that  they,  too,  were  once  strung 
upon  similar  threads  which  have  now  disappeared, 
leaving  the  stars  spaced  along  their  ancient  tracks. 
We  seem  forced  to  the  conclusion  that  there  was  a 
time  when  the  Pleiades  were  embedded  in  a  vast 
nebula  resembling  that  of  Orion,  and  that  the  cloud 
has  now  become  so  rare  by  gradual  condensation 
into  stars  that  the  merest  trace  of  it  remains,  and  this 
would  probably  have  escaped  detection  but  for  the 
remarkable  actinic  power  of  the  radiant  matter  of 
which  it  consists.  The  richness  of  many  of  these 
faint  nebulous  masses  in  ultra-violet  radiations, 
which  are  those  that  specially  affect  the  photographic 
plate,  is  the  cause  of  the  marvellous  revelatory  power 
of  celestial  photography.  So  the  veritable  unseen 
universe,  as  distinguished  from  the  "unseen  universe" 
of  metaphysical  speculation,  is  shown  to  us. 



A  different  kind  of  association  between  stars  and 
nebulae  is  shown  in  some  surprising  photographic 
objects  in  the  constellation  Cygnus,  where  long,  wispy 
nebulae,  billions  of  miles  in  length,  some  of  them 
looking  like  tresses  streaming  in  a  breeze,  lie  amid 
fields  of  stars  which  seem  related  to  them.  But  the 
relation  is  of  a  most  singular  kind,  for  notwithstand- 
ing the  delicate  structure  of  the  long  nebulae  they  ap- 
pear to  act  as  barriers,  causing  the  stars  to  heap 
themselves  on  one  side.  The  stars  are  two,  three,  or 
four  times  as  numerous  on  one  side  of  the  nebulae  as 
on  the  other.  These  nebulae,  as  far  as  appearance 
goes,  might  be  likened  to  rail  fences,  or  thin  hedges, 
against  which  the  wind  is  driving  drifts  of  powdery 
snow,  which,  while  scattered  plentifully  all  around, 
tends  to  bank  itself  on  the  leeward  side  of  the  ob- 
struction. The  imagination  is  at  a  loss  to  account 
for  these  extraordinary  phenomena;  yet  there  they 
are,  faithfully  giving  us  their  images  whenever  the 
photographic  plate  is  exposed  to  their  radiations. 

Thus  the  more  we  see  of  the  universe  with  improved 
methods  of  observation,  and  the  more  we  invent  aids 
to  human  senses,  each  enabling  us  to  penetrate  a 
little  deeper  into  the  unseen,  the  greater  becomes  the 
mystery.  The  telescope  carried  us  far,  photography 
is  carrying  us  still  farther;  but  what  as  yet  unimagined 
instrument  will  take  us  to  the  bottom,  the  top,  and 
the  end  ?  And  then,  what  hitherto  untried  power  of 
thought  will  enable  us  to  comprehend  the  meaning  of 
it  all? 



TO  the  untrained  eye  the  stars  and  the  planets  are 
not  distinguishable.  It  is  customary  to  call 
them  all  alike  ' 'stars/'  But  since  the  planets  more 
or  less  rapidly  change  their  places  in  the  sky,  in 
consequence  of  their  revolution  about  the  sun,  while 
the  stars  proper  seem  to  remain  always  in  the  same 
relative  positions,  the  latter  are  spoken  of  as  "fixed 
stars."  In  the  beginnings  of  astronomy  it  was  not 
known  that  the  "fixed  stars"  had  any  motion  in- 
dependent of  their  apparent  annual  revolution  with 
the  whole  sky  about  the  earth  as  a  seeming  centre. 
Now,  however,  we  know  that  the  term  "fixed  stars" 
is  paradoxical,  for  there  is  not  a  single  really  fixed 
object  in  the  whole  celestial  sphere.  The  apparent 
fixity  in  the  positions  of  the  stars  is  due  to  their  im- 
mense distance,  combined  with  the  shortness  of  the 
time  during  which  we  are  able  to  observe  them.  It 
is  like  viewing  the  plume  of  smoke  issuing  from  a 
steamer,  hull  down,  at  sea :  if  one  does  not  continue  to 
watch  it  for  a  long  time  it  appears  to  be  motionless, 
although  in  reality  it  may  be  travelling  at  great  speed 
across  the  line  of  sight.  Even  the  planets  seem  fixed 
in  position  if  one  watches  them  for  a  single  night  only, 
3  39 


and  the  more  distant  ones  do  not  sensibly  change  their 
places,  except  after  many  nights  of  observation. 
Neptune,  for  instance,  moves  but  little  more  than 
two  degrees  in  the  course  of  an  entire  year,  and  in  a 
month  its  change  of  place  is  only  about  one-third  of 
the  diameter  of  the  full  moon. 

Yet,  fixed  as  they  seem,  the  stars  are  actually 
moving  with  a  speed  in  comparison  with  which,  in 
some  cases,  the  planets  might  almost  be  said  to  stand 
fast  in  their  tracks.  Jupiter's  speed  in  his  orbit  is 
about  eight  miles  per  second,  Neptune's  is  less  than 
three  and  one-half  miles,  and  the  earth's  is  about 
eighteen  and  one-half  miles;  while  there  are  "fixed 
stars"  which  move  two  hundred  or  three  hundred 
miles  per  second.  They  do  not  all,  however,  move 
with  so  great  a  velocity,  for  some  appear  to  travel 
no  faster  than  the  planets.  But  in  all  cases,  notwith- 
standing their  real  speed,  long-continued  and  exceed- 
ingly careful  observations  are  required  to  demonstrate 
that  they  are  moving  at  all.  No  more  overwhelming 
impression  of  the  frightful  depths  of  space  in  which 
the  stars  are  buried  can  be  obtained  than  by  reflect- 
ing upon  the  fact  that  a  star  whose  actual  motion 
across  the  line  of  sight  amounts  to  two  hundred  miles 
per  second  does  not  change  its  apparent  place  in  the 
sky,  in  the  course  of  a  thousand  years,  sufficiently  to 
be  noticed  by  the  casual  observer  of  the  heavens! 

There  is  one  vast  difference  between  the  motions 
of  the  stars  and  those  of  the  planets  to  which  atten- 
tion should  at  once  be  called:  the  planets,  being  under 
the  control  of  a  central  force  emanating  from  their 
immediate  master,  the  sun,  all  move  in  the  same 



direction  and  in  orbits  concentric  about  the  sunj 
the  stars,  on  the  other  hand,  move  in  every  conceivable 
direction  and  have  no  apparent  centre  of  motion,  for 
all  efforts  to  discover  such  a  centre  have  failed.  At 
one  time,  when  theology  had  finally  to  accept  the 
facts  of  science,  a  grandiose  conception  arose  in  some 
pious  minds,  according  to  which  the  Throne  of  God 
was  situated  at  the  exact  centre  of  His  Creation,  and, 
seated  there,  He  watched  the  magnificent  spectacle 
of  the  starry  systems  obediently  revolving  around 
Him.  Astronomical  discoveries  and  speculations 
seemed  for  a  time  to  afford  some  warrant  for  this 
view,  which  was,  moreover,  an  acceptable  substitute 
for  the  abandoned  geocentric  theory  in  minds  that 
could  only  conceive  of  God  as  a  superhuman  artificer, 
constantly  admiring  His  own  work.  No  longer  ago 
than  the  middle  of  the  nineteenth  century  a  German 
astronomer,  Maedler,  believed  that  he  had  actually 
found  the  location .  of  the  centre  about  which  the 
stellar  universe  revolved.  He  placed  it  in  the  group 
of  the  Pleiades,  and  upon  his  authority  an  extraor- 
dinary imaginative  picture  was  sometimes  drawn  of 
the  star  Alcyone,  the  brightest  of  the  Pleiades,  as 
the  very  seat  of  the  Almighty.  This  idea  even  seemed 
to  gain  a  kind  of  traditional  support  from  the  mystic 
significance,  without  known  historical  origin,  which 
has  for  many  ages,  and  among  widely  separated 
peoples,  been  attached  to  the  remarkable  group  of 
which  Alcyone  is  the  chief.  But  since  Maedler's  i 
time  it  has  been  demonstrated  that  the  Pleiades 
cannot  be  the  centre  of  revolution  of  the  universe, 
and,  as  already  remarked,  all  attempts  to  find  or  fix 



such  a  centre  have  proved  abortive.  Yet  so  powerful 
was  the  hold  that  the  theory  took  upon  the  popular 
imagination,  that  even  to-day  astronomers  are  often 
asked  if  Alcyone  is  not  the  probable  site  of  "Jerusalem 
the  Golden." 

If  there  were  a  discoverable  centre  of  predominant 
gravitative  power,  to  which  the  motions  of  all  the 
stars  could  be  referred,  those  motions  would  ap- 
pear less  mysterious,  and  we  should  then  be  able 
to  conclude  that  the  universe  was,  as  a  whole,  a  proto- 
type of  the  subsidiary  systems  of  which  it  is  com- 
posed. We  should  look  simply  to  the  law  of  gravita- 
tion for  an  explanation,  and,  naturally,  the  centre 
would  be  placed  within  the  opening  enclosed  by  the 
Milky  Way.  If  it  were  there  the  Milky  Way  itself 
should  exhibit  signs  of  revolution  about  it,  like  a 
wheel  turning  upon  its  hub.  No  theory  of  the  star 
motions  as  a  whole  could  stand  which  failed  to  take 
account  of  the  Milky  Way  as  the  basis  of  all.  But 
the  very  form  of  that  divided  wreath  of  stars  forbids 
the  assumption  of  its  revolution  around  a  centre. 
Even  if  it  could  be  conceived  as  a  wheel  having  no 
material  centre  it  would  not  have  the  form  which  it 
actually  presents.  As  was  shown  in  Chapter  II,  there 
is  abundant  evidence  of  motion  in  the  Milky  Way; 
but  it  is  not  motion  of  the  system  as  a  whole,  but 
motion  affecting  its  separate  parts.  Instead  of  all 
moving  one  way,  the  galactic  stars,  as  far  as  their 
movements  can  be  inferred,  are  governed  by  local 
influences  and  conditions.  They  appear  to  travel 
crosswise  and  in  contrary  directions,  and  perhaps 
they  eddy  around  foci  where  great  numbers  have 



assembled;  but  of  a  universal  revolution  involving 
the  entire  mass  we  have  no  evidence. 

Most  of  our  knowledge  of  star  motions,  called  "  prop- 
er motions,"  relates  to  individual  stars  and  to  a  few 
groups  which  happen  to  be  so  near  that  the  effects 
of  their  movements  are  measurable.  In  some  cases 
the  motion  is  so  rapid  (not  in  appearance,  but  in 
reality)  that  the  chief  difficulty  is  to  imagine  how  it 
can  have  been  imparted,  and  what  will  eventually 
become  of  the  "runaways."  Without  a  collision, 
or  a  series  of  very  close  approaches  to  great  gravita- 
tive  centres,  a  star  travelling  through  space  at  the 
rate  of  two  hundred  or  three  hundred  miles  per  second 
could  not  be  arrested  or  turned  into  an  orbit  which 
would  keep  it  forever  flying  within  the  limits  of  the 
visible  universe.  A  famous  example  of  these  speed- 
ing stars  is  "1830  Groombridge,"  a  star  of  only  the 
sixth  magnitude,  and  consequently  just  visible  to  the 
naked  eye,  whose  motion  across  the  line  of  sight  is  so 
rapid  that  it  moves  upon  the  face  of  the  sky  a  distance 
equal  to  the  apparent  diameter  of  the  moon  every 
280  years.  The  distance  of  this  star  is  at  least 
200,000,000,000,000  miles,  and  may  be  two  or  three 
times  greater,  so  that  its  actual  speed  cannot  be  less 
than  two  hundred,  and  may  be  as  much  as  four  hun- 
dred, miles  per  second.  It  could  be  turned  into  a  new 
course  by  a  close  approach  to  a  great  sun,  but  it 
could  only  be  stopped  by  collision,  head-on,  with  a 
body  of  enormous  mass.  Barring  such  accidents  it 
must,  as  far  as  we  can  see,  keep  on  until  it  has  traversed 
our  stellar  system,  whence  it  may  escape  and  pass  out 
into  space  beyond,  to  join,  perhaps,  one  of  those 



other  universes  of  which  we  have  spoken.  Arcturus, 
one  of  the  greatest  suns  in  the  universe,  is  also  a  run- 
away, whose  speed  of  flight  has  been  estimated  all  the 
way  from  fifty  to  two  hundred  miles  per  second. 
Arcturus,  we  have  every  reason  to  believe,  possesses 
hundreds  of  times  the  mass  of  our  sun — think,  then, 
of  the  prodigious  momentum  that  its  motion  implies ! 
Sirius  moves  more  moderately,  its  motion  across  the 
line  of  sight  amounting  to  only  ten  miles  per  second, 
but  it  is  at  the  same  time  approaching  the  sun  at 
about  the  same  speed,  its  actual  velocity  in  space 
being  the  resultant  of  the  two  displacements. 

What  has  just  been  said  about  the  motion  of  Sirius 
brings  us  to  another  aspect  of  this  subject.     The 
fact  is,  that  in  every  case  of  stellar  motion  the  dis- 
placement that  we  observe  represents  only  a  part  of 
the  actual  movement  of  the  star  concerned.     There 
are  stars  whose  motion  carries  them  straight  toward 
or  straight  away  from  the  earth,  and  such  stars,  of 
course,  show  no  cross  motion.     But  the  vast  majority 
are  travelling  in  paths  inclined  from  a  perpendicular 
to  our  line  of  sight.    Taken  as  a  whole,  the  stars  may 
be  said  to  be  flying  about  like  the  molecules  in  a  mass 
1  of  gas.    The  discovery  of  the  radial  component  in  the 
movements  of  the  stars  is  due  to  the  spectroscope. 
J  If  a  star  is  approaching,  its  spectral  lines  are  shifted 
\  toward  the  violet  end  of  the  spectrum  by  an  amount 
,  depending  upon  the  velocity  of  approach ;   if  it  is 
;  receding,  the  lines  are  correspondingly  shifted  toward 
!  the  red  end.     Spectroscopic  observation,  then,  com- 
bined  with   micrometric   measurement   of  the  cross 
motion,  enables  us  to  detect  the  real  movement    of 



the  star  in  space.  Sometimes  it  happens  that  a 
star's  radial  movement  is  periodically  reversed;  first 
it  approaches,  and  then  it  recedes.  This  indicates 
that  it  is  revolving  around  a  near-by  companion,  which 
is  often  invisible,  and  superposed  upon  this  motion  is 
that  of  the  two  stars  concerned,  which  together  may 
be  approaching  or  receding  or  travelling  across  the 
line  of  sight.  Thus  the  complications  involved  in  the 
stellar  motions  are  often  exceedingly  great  and 

Yet  another  source  of  complication  exists  in  the 
movement  of  our  own  star,  the  sun.  There  is  no 
more  difficult  problem  in  astronomy  than  that  of 
disentangling  the  effects  of  the  solar  motion  from 
those  of  the  motions  of  the  other  stars.  But  the 
problem,  difficult  as  it  is,  has  been  solved,  and  upon  its 
solution  depends  our  knowledge  of  the  speed  and 
direction  of  the  movement  of  the  solar  system 
through  space,  for  of  course  the  sun  carries  its  planets 
with  it.  One  element  of  the  solution  is  found  in  the 
fact  that,  as  a  result  of  perspective,  the  stars  toward 
which  we  are  going  appear  to  move  apart  toward  all 
points  of  the  compass,  while  those  behind  appear  to 
close  up  together.  Then  the  spectroscopic  principle 
already  mentioned  is  invoked  for  studying  the  shift 
of  the  lines,  which  is  toward  the  violet  in  the  stars 
ahead  of  us  and  toward  the  red  in  those  that  we  are 
leaving  behind.  Of  course  the  effects  of  the  independ- 
ent motions  of  the  stars  must  be  carefully  excluded. 
The  result  of  the  studies  devoted  to  this  subject  is  to 
show  that  we  are  travelling  at  a  speed  of  twelve  to 
fifteen  miles  per  second  in  a  northerly  direction, 



toward  the  border  of  the  constellations  Hercules  and 
Lyra.  A  curious  fact  is  that  the  more  recent  esti- 
mates show  that  the  direction  is  not  very  much  out 
of  a  straight  line  drawn  from  the  sun  to  the  star 
Vega,  one  of  the  most  magnificent  suns  in  the  heavens. 
But  it  should  not  be  inferred  from  this  that  Vega 
is  drawing  us  on;  it  is  too  distant  for  its  gravitation  to 
have  such  an  effect. 

Many  unaccustomed  thoughts  are  suggested  by 
this  mighty  voyage  of  the  solar  system.  Whence 
have  we  come,  and  whither  do  we  go  ?  Every  year 
of  our  lives  we  advance  at  least  375,000,000  miles. 
Since  the  traditional  time  of  Adam  the  sun  has  led 
his  planets  through  the  wastes  of  space  no  less  than 
225,000,000,000  miles,  or  more  than  2400  times  the 
distance  that  separates  him  from  the  earth.  Go 
back  in  imagination  to  the  geologic  ages,  and  try  to 
comprehend  the  distance  over  which  the  earth  has 
flown.  Where  was  our  little  planet  when  it  emerged 
out  of  the  clouds  of  chaos  ?  Where  was  the  sun  when 
his  "thunder  march"  began?  What  strange  con- 
stellations shone  down  upon  our  globe  when  its 
masters  of  life  were  the  monstrous  beasts  of  the 
"Age  of  Reptiles?"  A  million  years  is  not  much  of 
a  span  of  time  in  geologic  reckoning,  yet  a  million 
years  ago  the  earth  was  farther  from  its  present  place 
in  space  than  any  of  the  stars  with  a  measurable 
parallax  are  now.  It  was  more  than  seven  times  as 
far  as  Sirius,  nearly  fourteen  times  as  far  as  Alpha 
Centauri,  three  times  as  far  as  Vega,  and  twice  as  far 
as  Arcturus.  But  some  geologists  demand  two 
hundred,  three  hundred,  even  one  thousand  million 



years  to  enable  them  to  account  for  the  evolutionary 
development  of  the  earth  and  its  inhabitants.  In  a 
thousand  million  years  the  earth  would  have  travelled 
farther  than  from  the  remotest  conceivable  depths 
of  the  Milky  Way! 

Other  curious  reflections  arise  when  we  think  of 
the  form  of  the  earth's  track  as  it  follows  the  lead 
of  the  sun,  in  a  journey  which  has  neither  known  be- 
ginning nor  conceivable  end.  There  are  probably 
many  minds  which  have  found  a  kind  of  consolation 
in  the  thought  that  every  year  the  globe  returns  to  the 
same  place,  on  the  same  side  of  the  sun.  This  idea 
may  have  an  occult  connection  with  our  traditional 
regard  for  anniversaries.  When  that  period  of  the 
year  returns  at  which  any  great  event  in  our  lives 
has  occurred  we  have  the  feeling  that  the  earth,  in  its 
annual  round,  has,  in  a  manner,  brought  us  back  to 
the  scene  of  that  event.  We  think  of  the  earth's 
orbit  as  a  well-worn  path  which  we  traverse  many 
times  in  the  course  of  a  lifetime.  It  seems  familiar 
to  us,  and  we  grow  to  have  a  sort  of  attachment  to  it. 
The  sun  we  are  accustomed  to  regard  as  a  fixed  centre 
in  space,  like  the  mill  or  pump  around  which  the 
harnessed  patient  mule  makes  his  endless  circuits. 
But  the  real  fact  is  that  the  earth  never  returns  to  the 
place  in  space  which  it  has  once  quitted.  In  con- 
sequence of  the  motion  of  the  sun  carrying  the  earth 
and  the  other  planets  along,  the  track  pursued  by  our 
globe  is  a  vast  spiral  in  space  continually  developing 
and  never  returning  upon  its  course.  It  is  probable 
that  the  tracks  of  the  sun  and  the  other  stars  are  also 
irregular,  and  possibly  spiral,  although,  as  far  as  can 



be  at  present  determined,  they  appear  to  be  prac- 
tically straight.  Every  star,  wherever  it  may  be 
situated,  is  attracted  by  its  fellow-stars  from  many 
sides  at  once,  and  although  the  force  is  minimized  by 
distance,  yet  in  the  course  of  many  ages  its  effects 
must  become  manifest. 

Looked  at  from  another  side,  is  there  not  something 
immensely  stimulating  and  pleasing  to  the  imagina- 
tion in  the  idea  of  so  stupendous  a  journey,  which 
makes  all  of  us  the  greatest  of  travellers?  In  the 
course  of  a  long  life  a  man  is  transported  through 
space  thirty  thousand  million  miles;  Halley's  Comet 
does  not  travel  one-quarter  as  far  in  making  one  of  its 
immense  circuits.  And  there  are  adventures  on  this 
voyage  of  which  we  are  just  beginning  to  learn  to 
take  account.  Space  is  full  of  strange  things,  and  the 
earth  must  encounter  some  of  them  as  it  advances 
through  the  unknown.  Many  singular  speculations 
have  been  indulged  in  by  astronomers  concerning  the 
possible  effects  upon  the  earth  of  the  varying  state  of 
the  space  that  it  traverses.  Even  the  alternation  of 
hot  and  glacial  periods  has  sometimes  been  ascribed  to 
this  source.  When  tropical  life  flourished  around 
the  poles,  as  the  remains  in  the  rocks  assure  us,  the 
needed  high  temperature  may,  it  has  been  thought, 
have  been  derived  from  the  presence  of  the  earth  in  a 
warm  region  of  space.  Then,  too,  there  is  a  certain 
interest  for  us  in  the  thought  of  what  our  familiar 
planet  has  passed  through.  We  cannot  but  admire 
it  for  its  long  journeying  as  we  admire  the  traveller 
who  comes  to  us  from  remote  and  unexplored  lands, 
or  as  we  gaze  with  a  glow  of  interest  upon  the  first 



locomotive  that  has  crossed  a  continent,  or  a  ship 
that  has  visited  the  Arctic  or  Antarctic  regions.  If 
we  may  trust  the  indications  of  its  present  course, 
the  earth,  piloted  by  the  sun,  has  come  from  the 
Milky  Way  in  the  far  south  and  may  eventually  rejoin 
that  mighty  band  of  stars  in  the  far  north. 

While  the  stars  in  general  appear  to  travel  inde- 
pendently of  one  another,  except  when  they  are 
combined  in  binary  or  trinary  systems,  there  are 
notable  exceptions  to  this  rule.  In  some  quarters  of 
the  sky  we  behold  veritable  migrations  of  entire 
groups  of  stars  whose  members  are  too  widely  sepa- 
rated to  show '  any  indications  of  revolution  about  a 
common  centre  of  gravity.  This  leads  us  back  again 
to  the  wonderful  group  of  the  Pleiades.  All  of  the 
principal  stars  composing  that  group  are  travelling  in 
virtually  parallel  lines.  Whatever  force  set  them 
going  evidently  acted  upon  all  alike.  This  might  be 
explained  by  the  assumption  that  when  the  original 
projective  force  acted  upon  them  they  were  more 
closely  united  than  they  are  at  present,  and  that  in 
drifting  apart  they  have  not  lost  the  impulse  of  the 
primal  motion.  Or  it  may  be  supposed  that  they  are 
carried  along  by  some  current  in  space,  although  it 
would  be  exceeding  difficult,  in  the  present  state  of 
our  knowledge,  to  explain  the  nature  of  such  a  current. 
Yet  the  theory  of  a  current  has  been  proposed.  As 
to  an  attractive  centre  around  which  they  might 
revolve,  none  has  been  found.  Another  instance  of 
similar  "star-drift"  is  furnished  by  five  of  the  seven 
stars  constituting  the  figure  of  the  "Great  Dipper." 
In  this  case  the  stars  concerned  are  separated  very 



widely,  the  two  extreme  ones  by  not  less  than  fifteen 
degrees,  so  that  the  idea  of  a  common  motion  would 
never  have  been  suggested  by  their  aspect  in  the  sky; 
and  the  case  becomes  the  more  remarkable  from  the 
fact  that  among  and  between  them  there  are  other 
stars,  some  of  the  same  magnitude,  which  do  not  share 
their  motion,  but  are  travelling  in  other  directions. 
Still  other  examples  of  the  same  phenomenon  are 
found  in  other  parts  of  the  sky.  Of  course,  in  the  case 
of  compact  star-clusters,  it  is  assumed  that  all  the 
members  share  a  like  motion  of  translation  through 
space,  and  the  same  is  probably  true  of  dense  star- 
swarms  and  star-clouds. 

The  whole  question  of  star-drift  has  lately  assumed 
a  new  phase,  inconsequence  of  the  investigations  of 
Kapteyn,  Dyson,  and  Eddington  on  the  "systematic 
motions  of  the  stars."  This  research  will,  it  is  hoped, 
lead  to  an  understanding  of  the  general  law  governing 
the  movements  of  the  whole  body  of  stars  constituting 
the  visible  universe.  Taking  about  eleven  hundred 
stars  whose  proper  motions  have  been  ascertained 
with  an  approach  to  certainty,  and  which  are  dis- 
tributed in  all  parts  of  the  sky,  it  has  been  shown 
that  there  exists  an  apparent  double  drift,  in  two  in- 
dependent streams,  moving  in  different  and  nearly 
opposed  directions.  The  apex  of  the  motion  of  what 
is  called  "Stream  I "  is  situated,  according  to  Professor 
Kapteyn,  in  right  ascension  85°,  declination  south 
11°,  which  places  it  just  south  of  the  constellation 
Orion;  while  the  apex  of  "Stream  II"  is  in  right 
ascension  260°,  declination  south  48°,  placing  it  in 
the  constellation  Ara,  south  of  Scorpio.  The  two 



apices  differ  very  nearly  180°  in  right  ascension  and 
about  120°  in  declination.  The  discovery  of  these 
vast  star-streams,  if  they  really  exist,  is  one  of  the 
most  extraordinary  in  modern  astronomy.  It  offers 
the  correlation  of  stellar  movements  needed  as  the 
basis  of  a  theory  of  those  movements,  but  it  seems 
far  from  revealing  a  physical  cause  for  them.  As 
projected  against  the  celestial  sphere  the  stars  form- 
ing the  two  opposite  streams  appear  intermingled, 
some  obeying  one  tendency  and  some  the  other.  As 
Professor  Dyson  has  said,  the  hypothesis  of  this  double 
movement  is  of  a  revolutionary  character,  and  calls 
for  further  investigation.  Indeed,  it  seems  at  first 
glance  not  less  surprising  than  would  be  the  observa- 
tion that  in  a  snow-storm  the  flakes  over  our  heads 
were  divided  into  two  parties  and  driving  across  each 
other's  course  in  nearly  opposite  directions,  as  if 
urged  by  interpenetrating  winds. 

But  whatever  explanation  may  eventually  be  found 
for  the  motions  of  the  stars,  the  knowledge  of  the 
existence  of  those  motions  must  always  afford  a  new 
charm  to  the  contemplative  observer  of  the  heavens, 
for  they  impart  a  sense  of  life  to  the  starry  system 
that  would  otherwise  be  lacking.  A  stagnant  universe, 
with  every  star  fixed  immovably  in  its  place,  would 
not  content  the  imagination  or  satisfy  our  longing 
for  ceaseless  activity.  The  majestic  grandeur  of  the 
evolutions  of  the  celestial  hosts,  the  inconceivable 
vastness  of  the  fields  of  space  in  which  they  are 
executed,  the  countless  numbers,  the  immeasurable 
distances,  the  involved  convolutions,  the  flocking 
and  the  scattering,  the  interpenetrating  marches  and 


countermarches,  the  strange  community  of  impulsion 
affecting  stars  that  are  wide  apart  in  space  and  caus- 
ing them  to  traverse  the  general  movement  about 
them  like  aides  and  despatch-bearers  on  a  battle- 
field— all  these  arouse  an  intensity  of  interest  which  is 
heightened  by  the  mystery  behind  them. 



FROM  a  historical  and  picturesque  point  of  view, 
one  of  the  most  striking  results  of  the  motions 
of  the  stars  described  in  the  last  chapter  is  their  effect 
upon  the  forms  of  the  constellations,  which  have  been 
watched  and  admired  by  mankind  from  a  period  so 
early  that  the  date  of  their  invention  is  now  unknown. 
The  constellations  are  formed  by  chance  combina- 
tions of  conspicious  stars,  like  figures  in  a  kaleidoscope, 
and  if  our  lives  were  commensurate  with  the  aeons  of 
cosmic  existence  we  should  perceive  that  the  kaleido- 
scope of  the  heavens  was  ceaselessly  turning  and  throw- 
ing the  stars  into  new  symmetries.  Even  if  the  stars 
stood  fast,  the  motion  of  the  solar  system  would 
gradually  alter  the  configurations,  as  the  elements  of 
a  landscape  dissolve  and  recombine  in  fresh  group- 
ings with  the  traveller's  progress  amid  them.  But 
with  the  stars  themselves  all  in  motion  at  various 
speeds  and  in  many  directions,  the  changes  occur  more 
rapidly.  Of  course,  "rapid"  is  here  to  be  understood 
in  a  relative  sense ;  the  wheel  of  human  history  to  an 
eye  accustomed  to  the  majestic  progression  of  the 
universe  would  appear  to  revolve  with  the  velocity 
of  a  whirling  dynamo.  Only  the  deliberation  of  geo- 



logical  movements  can  be  contrasted  with  the  evolu- 
tion and  devolution  of  the  constellations. 

And  yet  this  secular  fluctuation  of  the  constellation 
figures  is  not  without  keen  interest  for  the  meditative 
observer.  It  is  another  reminder  of  the  swift  muta- 
bility of  terrestrial  affairs.  To  the  passing  glance, 
which  is  all  that  we  can  bestow  upon  these  figures,  they 
appear  so  immutable  that  they  have  been  called  into 
service  to  form  the  most  lasting  records  of  ancient 
thought  and  imagination  that  we  possess.  In  the 
forms  of  the  constellations,  the  most  beautiful,  and,  in 
imaginative  quality,  the  finest,  mythology  that  the 
world  has  ever  known  has  been  perpetuated.  Yet,  in 
a  broad  sense,  this  scroll  of  human  thought  imprinted 
on  the  heavens  is  as  evanescent  as  the  summer  clouds. 
Although  more  enduring  than  parchment,  tombs, 
pyramids,  and  temples,  it  is  as  far  as  they  from  truly 
eternizing  the  memory  of  what  man  has  fancied  and 

Before  studying  the  effects  that  the  motions  of  the 
stars  have  had  and  will  have  upon  the  constellations, 
it  is  worth  while  to  consider  a  little  further  the  im- 
portance of  the  stellar  pictures  as  archives  of  history. 
To  emphasize  the  importance  of  these  effects  it  is  only 
necessary  to  recall  that  the  constellations  register 
the  oldest  traditions  of  our  race.  In  the  history  of 
primeval  religions  they  are  the  most  valuable  of  docu- 
ments. Leaving  out  of  account  for  the  moment  the 
more  familiar  mythology  of  the  Greeks,  based  on 
something  older  yet,  we  may  refer  for  illustration  to 
that  of  the  mysterious  Maya  race  of  America.  At 
Izamal,  in  Yucatan,  says  Mr.  Stansbury  Hagar,  is 



a  group  of  ruins  perched,  after  the  Mexican  and 
Central- American  plan,  on  the  summits  of  pyramidal 
mounds  which  mark  the  site  of  an  ancient  theogonic 
centre  of  the  Mayas.  Here  the  temples  all  evi- 
dently refer  to  a  cult  based  upon  the  constellations  as 
symbols.  The  figures  and  the  names,  of  course,  were 
not  the  same  as  those  that  we  have  derived  from  our 
Aryan  ancestors,  but  the  star  groups  were  the  same 
or  nearly  so.  For  instance,  the  loftiest  of  the  temples 
at  Izamal  was  connected  with  the  sign  of  the  con- 
stellation known  to  us  as  Cancer,  marking  the  place 
of  the  sun  at  the  summer  solstice,  at  which  period  the 
sun  was  supposed  to  descend  at  noon  like  a  great  bird 
of  fire  and  consume  the  offerings  left  upon  the  altar. 
Our  Scorpio  was  known  to  the  Mayas  as  the  sign  of 
the  "Death  God."  Our  Libra,  the  "Balance,"  with 
which  the  idea  of  a  divine  weighing  out  of  justice  has 
always  been  connected,  seems  to  be  identical  with  the 
Mayan  constellation  Teoyaotlatohua  with  which  was 
associated  a  temple  where  dwelt  the  priests  whose 
special  business  it  was  to  administer  justice  and  to 
foretell  the  future  by  means  of  information  obtained 
from  the  spirits  of  the  dead.  Orion,  the  "Hunter" 
of  our  celestial  mythology,  was  among  the  Mayas  a 
"Warrior,"  while  Sagittarius  and  others  of  our  con- 
stellations were  known  to  them  (under  different  names, 
of  course),  and  all  were  endowed  with  a  religious 
symbolism.  And  the  same  star  figures,  having  the 
same  significance,  were  familiar  to  the  Peruvians,  as 
shown  by  the  temples  at  Cuzco.  Thus  the  imagina- 
tion of  ancient  America  sought  in  the  constellations 
symbols  of  the  unchanging  gods. 
*  55 


But,  in  fact,  there  is  no  nation  and  no  people  that 
has  not  recognized  the  constellations,  and  at  one 
period  or  another  in  its  history  employed  them  in 
some  symbolic  or  representative  capacity.  As  han- 
dled by  the  Greeks  from  prehistoric  times,  the  con- 
stellation myths  became  the  very  soul  of  poetry.  The 
imagination  of  that  wonderful  race  idealized  the 
principal  star  groups  so  effectively  that  the  figures 
and  traditions  thus  attached  to  them  have,  for  civil- 
ized mankind,  displaced  all  others,  just  as  Greek  art 
in  its  highest  forms  stands  without  parallel  and 
eclipses  every  rival.  The  Romans  translated  no 
heroes  and  heroines  of  the  mythical  period  of  their 
history  to  the  sky,  and  the  deified  Ca3sars  never  en- 
tered that  lofty  company,  but  the  heavens  are  filled 
with  the  early  myths  of  the  Greeks.  Herakles  nightly 
resumes  his  mighty  labors  in  the  stars;  Zeus,  in  the 
form  of  the  white  "Bull,"  Taurus,  bears  the  fair 
Europa  on  his  back  through  the  celestial  waves; 
Andromeda  stretches  forth  her  shackled  arms  in  the 
star-gemmed  ether,  beseeching  aid ;  and  Perseus,  in  a 
blaze  of  diamond  armor,  revives  his  heroic  deeds  amid 
sparkling  clouds  of  stellar  dust.  There,  too,  sits  Queen 
Cassiopeia  in  her  dazzling  chair,  while  the  Great 
King,  Cepheus,  towers  gigantic  over  the  pole.  Pro- 
fessor Young  has  significantly  remarked  that  a  great 
number  of  the  constellations  are  connected  in  some 
way  or  other  with  the  Argonautic  Expedition — that 
strangely  fascinating  legend  of  earliest  Greek  story 
which  has  never  lost  its  charm  for  mankind.  In  view 
of  all  this,  we  may  well  congratulate  ourselves  that  the 
constellations  will  outlast  our  time  and  the  time  of 



countless  generations  to  follow  us;  and  yet  they  are 
very  far  from  being  eternal.  Let  us  now  study  some 
of  the  effects  of  the  stellar  motions  upon  them. 

We  begin  with  the  familiar  figure  of  the  "Great 
Dipper."  He  who  has  not  drunk  inspiration  from 
its  celestial  bowl  is  not  yet  admitted  to  the  circle  of 
Olympus.  This  figure  is  made  up  of  seven  con- 
spicuous stars  in  the  constellation  Ursa  Major,  the 
" Greater  Bear."  The  handle  of  the  "Dipper"  cor- 
responds to  the  tail  of  the  imaginary  "Bear,"  and  the 
bowl  lies  upon  his  flank.  In  fact,  the  figure  of  a  dipper 
is  so  evident  and  that  of  a  bear  so  unevident,  that  to 
most  persons  the  "Great  Dipper"  is  the  only  part  of 
the  constellation  that  is  recognizable.  Of  the  seven 
stars  mentioned,  six  are  of  nearly  equal  brightness, 
ranking  as  of  the  second  magnitude,  while  the  seventh 
is  of  only  the  third  magnitude.  The  difference  is  very 
striking,  since  every  increase  of  one  magnitude  in- 
volves an  increase  of  two-and-a-half  times  in  bright- 
ness. There  appears  to  be  little  doubt  that  the  faint 
star,  which  is  situated  at  the  junction  of  the  bowl 
and  the  handle,  is  a  variable  of  long  period,  since 
three  hundred  years  ago  it  was  as  bright  as  its  com- 
panions. But  however  that  may  be,  its  relative  faint- 
ness  at  the  present  time  interferes  but  little  with  the 
perfection  of  the  "Dipper's"  figure.  In  order  the 
more  readily  to  understand  the  changes  wrhich  are 
taking  place,  it  will  be  well  to  mention  both  the  names 
and  the  Greek  letters  which  are  attached  to  the  seven 
stars.  Beginning  at  the  star  in  the  upper  outer  edge 
of  the  rim  of  the  bowl  and  running  in  regular  order 
round  the  bottom  and  then  out  to  the  end  of  the  handle, 



the  names  and  letters  are  as  follows:  Dubhe  (a), 
Merak  (j3),  Phaed  (7),  Megrez  (8),  Alioth  (e), 
Mizar  (c),  and  Benetnasch  (ij).  Megrez  is  the  faint 
star  already  mentioned  at  the  junction  of  the  bowl 
and  handle,  and  Mizar,  in  the  middle  of  the  handle,  has 
a  close,  naked-eye  companion  which  is  named  Alcor. 

THE    "GREAT    DIPPER"   AS   IT   IS 





The  Arabs  called  this  singular  pair  of  stars  ''The 
Horse  and  Rider."  Merak  and  Dubhe  are  called 
4 'The  Pointers,"  because  an  imaginary  line  drawn 
northward  through  them  indicates  the  Pole  Star. 

Now  it  has  been  found  that  five  of  these  stars — viz., 
Merak,  Phaed,  Megrez,  Alioth,  and  Mizar  (with  its 
comrade) — are  moving  with  practically  the  same  speed 
in  an  easterly  direction,  while  the  other  two,  Dubhe 
and  Benetnasch,  are  simultaneously  moving  west- 
ward, the  motion  of  Benetnasch  being  apparently 
the  more  rapid.  The  consequence  of  these  opposed 
motions  is,  of  course,  that  the  figure  of  the  "Dipper" 
cannot  always  have  existed  and  will  not  continue  to 
exist.  In  the  accompanying  diagrams  it  has  been 
thought  interesting  to  show  the  relative  positions  of 
these  seven  stars,  as  seen  from  the  point  which  the 
earth  now  occupies,  both  in  the  past  and  in  the  future. 
Arrows  attached  to  the  stars  in  the  figure  representing 
the  present  appearance  of  the  "Dipper"  indicate  the 
directions  of  the  motions  and  the  distances  over  which 
they  will  carry  the  stars  in  a  period  of  about  five 
hundred  centuries.  The  time,  no  doubt,  seems  long, 
but  remember  the  vast  stretch  of  ages  through  which 
the  earth  has  passed,  and  then  reflect  that  no  reason 
is  apparent  why  our  globe  should  not  continue  to  be 
a  scene  of  animation  for  ten  thousand  centuries  yet 
to  come.  The  fact  that  the  little  star  Alcor  placed 
so  close  to  Mizar  should  accompany  the  latter  in  its 
flight  is  not  surprising,  but  that  two  of  the  principal 
stars  of  the  group  should  be  found  moving  in  a  direc- 
tion exactly  opposed  to  that  pursued  by  the  other  five 
is  surprising  in  the  highest  degree;  and  it  recalls  the 



strange  theory  of  a  double  drift  affecting  all  the  stars, 
to  which  attention  was  called  in  the  preceding  chapter. 
It  would  appear  that  Benetnasch  and  Dubhe  belong 



to  one  "current,"  and  Merak,  Phaed,  Megrez,  Alioth, 
and  Mizar  to  the  other.  As  far  as  is  known,  the  mo- 
tions of  the  seven  stars  are  not  shared  by  the  smaller 



stars  scattered  about  them,  but  on  the  theory  of  cur- 
rents there  should  be  such  community  of  motion, 
and  further  investigation  may  reveal  it. 

From  the  "Great  Dipper"  we  turn  to  a  constella- 
tion hardly  less  conspicuous  and  situated  at  an  equal 
distance  from  the  pole  on  the  other  side — Cassiopeia. 
This  famous  star-group  commemorating  the  romantic 
Queen  of  Ethiopia  whose  vain  boasting  of  her  beauty 
was  punished  by  the  exposure  of  her  daughter 
Andromeda  to  the  "Sea  Monster,"  is  well  marked 
by  five  stars  which  form  an  irregular  letter  "W" 
with  its  open  side  toward  the  pole.  Three  of  these 
stars  are  usually  ranked  as  of  the  second  magnitude, 
and  two  of  the  third;  but  to  ordinary  observation 
they  appear  of  nearly  equal  brightness,  and  present 
a  very  striking  picture.  They  mark  out  the  chair 
and  a  part  of  the  figure  of  the  beautiful  queen.  Be- 
ginning at  the  right-hand,  or  western,  end  of  the 
"W,"  their  Greek  letter  designations  are:  Beta  (j3), 
Alpha  (a),  Gamma  (y),  Delta  (S),  and  Epsilon  (e). 
Four  of  them,  Beta,  Alpha,  Delta,  and  Epsilon  are 
travelling  eastwardly  at  various  speeds,  while  the  fifth, 
Gamma,  moves  in  a  westerly  direction.  The  motion 
of  Beta  is  more  rapid  than  that  of  any  of  the  others. 
It  should  be  said,  however,  that  no  little  uncertainty 
attaches  to  the  estimates  of  the  rate  of  motion  of 
stars  which  are  not  going  very  rapidly,  and  different 
observers  often  vary  considerably  in  their  results. 

In  the  beautiful  "Northern  Crown,"  one  of  the 
most  perfect  and  charming  of  all  the  figures  to  be 
found  in  the  stars,  the  alternate  combining  and 
scattering  effects  of  the  stellar  motions  are  shown  by 



comparing  the  appearance  which  the  constellation 
must  have  had  five  hundred  centuries  ago  with  that 
which  it  has  at  present  and  that  which  it  will  have 
in  the  future.  The  seven  principal  stars  of  the 
asterism,  forming  a  surprisingly  perfect  coronet,  have 
movements  in  three  directions  at  right  angles  to  one 
another.  That  in  these  circumstances  they  should 
ever  have  arrived  at  positions  giving  them  so  striking 
an  appearance  of  definite  association  is  certainly 
surprising;  from  its  aspect  one  would  have  expected 
to  find  a  community  of  movement  governing  the 
brilliants  of  the  " Crown,"  but  instead  of  that  we  find 
evidence  that  they  will  inevitably  drift  apart  and  the 
beautiful  figure  will  dissolve. 

A  similar  fate  awaits  such  asterisms  as  the  "North- 
ern Cross"  in  Cygnus;  the  "Crow"  (Corvus),  which 
stands  on  the  back  of  the  great  "Sea  Serpent," 
Hydra,  and  pecks  at  his  scales;  "Job's  Coffin" 
(Delphinus);  the  "Great  Square  of  Pegasus";  the 
"Twins"  (Gemini) ;  the  beautiful  "Sickle"  in  Leo;  and 
the  exquisite  group  of  the  Hyades  in  Taurus.  In  the 
case  of  the  Hyades,  two  controlling  movements  are 
manifest:  one,  affecting  five  of  the  stars  which  form 
the  well-known  figure  of  a  letter  "V,"  is  directed 
northerly;  the  other,  which  controls  the  direction  of 
two  stars,  has  an  easterly  trend.  The  chief  star  of 
the  group,  Aldebaran,  one  of  the  finest  of  all  stars 
both  for  its  brilliance  and  its  color,  is  the  most  affect- 
ed by  the  easterly  motion.  In  time  it  will  drift  en- 
tirely out  of  connection  with  its  present  neighbors. 
Although  the  Hyades  do  not  form  so  compact  a  group 
as  the  Pleiades  in  the  same  constellation,  yet  their 



appearance  of  relationship  is  sufficient  to  awaken  a 
feeling  of  surprise  over  the  fact  that,  as  with  the  stars 
of  the  "Dipper,"  their  association  is  only  temporary  or 


THE    "  NORTHERN    CROWN  "    AT 

The  Pearl 



The  Pearl 


The  great  figure  of  Orion  appears  to  be  more  last- 
ing, not  because  its  stars  are  physically  connected, 
but  because  of  their  great  distance,  which  renders 



their  movements  too  deliberate  to  be  exactly  ascer- 
tained. Two  of  the  greatest  of  its  stars,  Betelgeusc 
and  Rigel,  possess,  as  far  as  has  been  ascertained, 
no  perceptible  motion  across  the  line  of  sight,  but 
there  is  a  little  movement  perceptible  in  the  "Belt." 
At  the  present  time  this  consists  of  an  almost  perfect 
straight  line,  a  row  of  second-magnitude  stars  about 
equally  spaced  and  of  the  most  striking  beauty.  In 
the  course  of  time,  however,  the  two  right-hand 
stars,  Mintaka  and  Alnilam  (how  fine  are  these  Arabic 
star  names!)  will  approach  each  other  and  form  a 
naked-eye  double,  but  the  third,  Alnita,  will  drift 
away  eastward,  so  that  the  "Belt"  will  no  longer 

For  one  more  example,  let  us  go  to  the  southern 
hemisphere,  whose  most  celebrated  constellation, 
the  "Southern  Cross,"  has  found  a  place  in  all  modern 
literatures,  although  it  has  no  claim  to  consideration 
on  account  of  association  with  ancient  legends.  This 
most  attractive  asterism,  which  has  never  ceased  to 
fascinate  the  imagination  of  Christendom  since  it  was 
first  devoutly  described  by  the  early  explorers  of  the 
South,  is  but  a  passing  collocation  of  brilliant  stars. 
Yet  even  in  its  transfigurations  it  has  been  for  hun- 
dreds of  centuries,  and  will  continue  to  be  for  hun- 
dreds of  centuries  to  come,  a  most  striking  object  in 
the  sky.  Our  figures  show  its  appearance  in  three 
successive  phases :  first,  as  it  was  fifty  thousand  years 
ago  (viewed  from  the  earth's  present  location) ;  second, 
as  it  is  in  our  day ;  and,  third,  as  it  will  be  an  equal  time 
in  the  future.  The  nearness  of  these  bright  stars  to 
one  another — the  length  of  the  longer  beam  of  the 



"Cross"  is  only  six  degrees — makes  this  group  very 
noticeable,  whatever  the  arrangement  of  its  com- 
ponents may  be.  The  largest  star,  at  the  base  of  the 
"Cross,"  is  of  the  first  magnitude,  two  of  the  others 
are  of  the  second  magnitude,  and  the  fourth  is  of 
the  third.  Other  stars,  not  represented  in  the  figures, 


AS    IT   IS  AS    IT   WILL  BE 

THE   "  SOUTHERN    CROSS  "    AS   IT   ONCE    WAS 

increase  the  effect  of  a  celestial  blazonry,  although 
they  do  not  help  the  resemblance  to  a  cross. 

But  since  the  motion  of  the  solar  system  itself  will, 
in  the  course  of  so  long  a  period  as  fifty  thousand 
years,  produce  a  great  change  in  the  perspective  of 
the  heavens  as  seen  from  the  earth,  by  carrying  us 
nearly  nineteen  trillion  miles  from  our  present  place, 



why,  it  may  be  asked,  seek  to  represent  future  ap- 
pearances of  the  constellations  which  we  could  not 
hope  to  see,  even  if  we  could  survive  so  long?  The 
answer  is :  Because  these  things  aid  the  mind  to  form 
a  picture  of  the  effects  of  the  mobility  of  the  starry 
universe.  Only  by  showing  the  changes  from  some 
definite  point  of  view  can  we  arrive  at  a  due  com- 
prehension of  them.  The  constellations  are  more  or 
less  familiar  to  everybody,  so  that  impending  changes 
of  their  forms  must  at  once  strike  the  eye  and  the 
imagination,  and  make  clearer  the  significance  of  the 
movements  of  the  stars.  If  the  future  history  of 
mankind  is  to  resemble  its  past  and  if  our  race  is 
destined  to  survive  yet  a  million  years,  then  our 
remote  descendants  will  see  a  "new  heavens"  if  not 
a  "new  earth,"  and  will  have  to  invent  novel  con- 
stellations to  perpetuate  their  legends  and  my- 

If  our  knowledge  of  the  relative  distances  of  the 
stars  were  more  complete,  it  would  be  an  interesting 
exercise  in  celestial  geometry  to  project  the  con- 
stellations probably  visible  to  the  inhabitants  of 
worlds  revolving  around  some  of  the  other  suns  of 
space.  Our  sun  is  too  insignificant  for  us  to  think 
that  he  can  make  a  conspicuous  appearance  among 
them,  except,  perhaps,  in  a  few  cases.  As  seen, 
for  instance,  from  the  nearest  known  star,  Alpha 
Centauri,  the  sun  would  appear  of  the  average  first 
magnitude,  and  consequently  from  that  standpoint 
he  might  be  the  gem  of  some  little  constellation  which 
had  no  Sirius,  or  Arcturus,  or  Vega  to  eclipse  him  with 
its  superior  splendor.  But  from  the  distance  of  the 



vast  majority  of  the  stars  the  sun  would  probably  be 
invisible  to  the  naked  eye,  and  as  seen  from  nearer 
systems  could  only  rank  as  a  fifth  or  sixth  magnitude 
star,  unnoticed  and  unknown  except  by  the  star- 
charting  astronomer. 


SUPPOSE  it  were  possible  for  the  world  to  take 
fire  and  burn  up — as  some  pessimists  think  that 
it  will  do  when  the  Divine  wrath  shall  have  sufficiently 
accumulated  against  it — nobody  out  of  our  own  little 
corner  of  space  would  ever  be  aware  of  the  catastrophe ! 
With  all  their  telescopes,  the  astronomers  living  in  the 
golden  light  of  Arcturus  or  the  diamond  blaze  of 
Canopus  would  be  unable  to  detect  the  least  glimmer 
of  the  conflagration  that  had  destroyed  the  seat  of 
Adam  and  his  descendants,  just  as  now  they  are 
totally  ignorant  of  its  existence. 

But  at  least  fifteen  times  in  the  course  of  recorded 
history  men  looking  out  from  the  earth  have  beheld 
in  the  remote  depths  of  space  great  outbursts  of  fiery 
light,  some  of  them  more  splendidly  luminous  than 
anything  else  in  the  firmament  except  the  sun!  If 
they  were  conflagrations,  how  many  million  worlds 
like  ours  were  required  to  feed  their  blaze  ? 

It  is  probable  that  " temporary"  or  "new"  stars, 
as  these  wonderful  apparitions  are  called,  really  are 
conflagrations;  not  in  the  sense  of  a  bonfire  or  a  burn- 
ing house  or  city,  but  in  that  of  a  sudden  eruption  of 
inconceivable  heat  and  light,  such  as  would  result 



from  the  stripping  off  the  shell  of  an  encrusted  sun 
or  the  crashing  together  of  two  mighty  orbs  flying 
through  space  with  a  hundred  times  the  velocity  of 
the  swiftest  cannon-shot. 

Temporary  stars  are  the  rarest  and  most  erratic 
of  astronomical  phenomena.  The  earliest  records 
relating  to  them  are  not  very  clear,  and  we  cannot  in 
every  instance  be  certain  that  it  was  one  of  these 
appearances  that  the  ignorant  and  superstitious  old 
chroniclers  are  trying  to  describe.  The  first  tem- 
porary star  that  we  are  absolutely  sure  of  appeared 
in  1572,  and  is  known  as  "Tycho's  Star,"  because  the 
celebrated  Danish  astronomer  (whose  remains,  with 
his  gold-and-silver  artificial  nose — made  necessary 
by  a  duel — still  intact,  were  disinterred  and  reburied 
in  1901)  was  the  first  to  perceive  it  in  the  sky,  and  the 
most  assiduous  and  successful  in  his  studies  of  it. 
As  the  first  fully  accredited  representative  of  its  class, 
this  new  star  made  its  entry  upon  the  scene  with 
becoming  eclat.  It  is  characteristic  of  these  phenom- 
ena that  they  burst  into  view  with  amazing  sudden- 
ness, and,  of  course,  entirely  unexpectedly.  Tycho's 
star  appeared  in  the  constellation  Cassiopeia,  near 
a  now  well-known  and  much- watched  little  star  named 
Kappa,  on  the  evening  of  November  n,  1572.  The 
story  has  often  been  repeated,  but  it  never  loses  in- 
terest, how  Tycho,  going  home  that  evening,  saw 
people  in  the  street  pointing  and  staring  at  the 
sky  directly  over  their  heads,  and  following  the  direc- 
tion of  their  hands  and  eyes  he  was  astonished  to  see, 
near  the  zenith,  an  unknown  star  of  surpassing  brill- 
iance. It  outshone  the  planet  Jupiter,  and  was  there- 



fore  far  brighter  than  the  first  magnitude.  There  was 
not  another  star  in  the  heavens  that  could  be  compared 
with  it  in  splendor.  Tycho  was  not  in  all  respects  free 
from  the  superstitions  of  his  time — and  who  is  ? — but 
he  had  the  true  scientific  instinct,  and  immediately  he 
began  to  study  the  stranger,  and  to  record  with  the 
greatest  care  every  change  in  its  aspect.  First  he  de- 
termined as  well  as  he  could  with  the  imperfect  in- 
struments of  his  day,  many  of  which  he  had  himself 
invented,  the  precise  location  of  the  phenomenon  in 
the  sky.  Then  he  followed  the  changes  that  it  under- 
went. At  first  it  brightened  until  its  light  equalled 
or  exceeded  that  of  the  planet  Venus  at  her  bright- 
est, a  statement  which  will  be  appreciated  at  its  full 
value  by  any  one  who  has  ever  watched  Venus  when 
she  plays  her  dazzling  role  of  "Evening  Star,"  flaring 
like  an  arc  light  in  the  sunset  sky.  It  even  became 
so  brilliant  as  to  be  visible  in  full  daylight,  since,  its 
position  being  circumpolar,  it  never  set  in  the  latitude 
of  Northern  Europe.  Finally  it  began  to  fade,  turn- 
ing red  as  it  did  so,  and  in  March,  1574,  it  disappeared 
from  Tycho's  searching  gaze,  and  has  never  been  seen 
again  from  that  day  to  this.  None  of  the  astronomers 
of  the  time  could  make  anything  of  it.  They  had  not 
yet  as  many  bases  of  speculation  as  we  possess  to-day. 
Tycho's  star  has  achieved  a  romantic  reputation  by 
being  fancifully  identified  with  the  "Star  of  Bethle- 
hem, "  said  to  have  led  the  wrondering  Magi  from  their 
eastern  deserts  to  the  cradle-manger  of  the  Savior  in 
Palestine.  Many  attempts  have  been  made  to 
connect  this  traditional  "star"  with  some  known 
phenomenon  of  the  heavens,  and  none  seems  more 


\          5 

\                                                                 ^       * 

v                                                               x     ,       * 

\                                                       \  • 

\                                                                            \ 

\                                                                           /  >-  

\                                                                       /     « 

\                                                                    / 

\                                                                / 

\              Camelopardalis               / 


\                 •   /  ^>^ 


/     '  \ 

\                                    /                          x 


c          v                         '    * 

•      • 

e//a      \                               t 

.---'  _    /       **        •* 

/'  •  '           "^        *t  *r 


.*    i   \ 

Perseus           w                              \ 


\,  •  N 



,\          Cassiopeia 

CHART    SHOWING    LOCATION    OF    TYCHO's    STAR,    1572,    AND    NOVA 
PERSEI   OF    1901 


idle  than  this.  Yet  it  persistently  survives,  and  no 
astronomer  is  free  from  eager  questions  about  it  ad- 
dressed by  people  whose  imagination  has  been  excited 
by  the  legend.  It  is  only  necessary  to  say  that  the 
supposition  of  a  connection  between  the  phenomenon 
of  the  Magi  and  Tycho's  star  is  without  any  scien- 
tific foundation.  It  was  originally  based  upon  an 
unwarranted  assumption  that  the  star  of  Tycho  was 
a  variable  of  long  period,  appearing  once  every  three 
hundred  and  fifteen  years,  or  thereabout.  If  that 
were  true  there  would  have  been  an  apparition  some- 
where near  the  traditional  date  of  the  birth  of  Christ, 
a  date  which  is  itself  uncertain.  But  even  the  data 
on  which  the  assumption  was  based  are  inconsistent 
with  the  theory.  Certain  monkish  records  speak  of 
something  wonderful  appearing  in  the  sky  in  the  years 
1264  and  945,  and  these  were  taken  to  have  been 
outbursts  of  Tycho's  star.  Investigation  shows  that 
the  records  more  probably  refer  to  comets,  but  even 
if  the  objects  seen  were  temporary  stars,  their  dates 
do  not  suit  the  hypothesis;  from  945  to  1264  there  is 
a  gap  of  319  years,  and  from  1264  to  1572  one  of  only 
308  years;  moreover,  337  years  have  now  (1909) 
elapsed  since  Tycho  saw  the  last  glimmer  of  his  star. 
Upon  a  variability  so  irregular  and  uncertain  as  that, 
even  if  we  felt  sure  that  it  existed,  no  conclusion  could 
be  found  concerning  an  apparition  occurring  2000 
years  ago. 

In  the  year  1600  (the  year  in  which  Giordano  Bruno 

was  burned  at  the  stake  for  teaching  that  there  is 

more  than  one  physical  world) ,  a  temporary  star  of  the 

third  magnitude  broke  out  in  the  constellation  Cygnus, 

V  73 


and  curiously  enough,  considering  the  rarity  of  such 
phenomena,  only  four  years  later  another  surprisingly 
brilliant  one  appeared  in  the  constellation  Ophiuchus. 
This  is  of  ten  called  "  Kepler's  Star/'  because  the  great 
German  astronomer  devoted  to  it  the  same  attention 
that  Tycho  had  given  to  the  earlier  phenomenon. 
It,  too,  like  Tycho's,  was  at  first  the  brightest  object 
in  the  stellar  heavens,  although  it  seems  never  to  have 
quite  equalled  its  famous  predecessor  in  splendor. 
It  disappeared  after  a  year,  also  turning  of  a  red  color 
as  it  became  more  faint.  We  shall  see  the  significance 
of  this  as  we  go  on.  Some  of  Kepler's  contemporaries 
suggested  that  the  outburst  of  this  star  was  due  to  a 
meeting  of  atoms  in  space,  an  idea  bearing  a  striking 
resemblance  to  the  modern  theory  of  "astronomical 

In  1670,  1848,  and  1860  temporary  stars  made  their 
appearance,  but  none  of  them  was  of  great  brilliance. 
In  1866  one  of  the  second  magnitude  broke  forth  in 
the  "Northern  Crown"  and  awoke  much  interest, 
because  by  that  time  the  spectroscope  had  begun 
to  be  employed  in  studying  the  composition  of  the 
stars,  and  Huggins  demonstrated  that  the  new  star 
consisted  largely  of  incandescent  hydrogen.  But 
this  star,  apparently  unlike  the  others  mentioned,  was 
not  absolutely  new.  Before  its  outburst  it  had  shone 
as  a  star  of  the  ninth  magnitude  (entirely  invisible, 
of  course,  to  the  naked  eye) ,  and  after  about  six  weeks 
it  faded  to  its  original  condition  in  which  it  has 
ever  since  remained.  In  1876  a  temporary  star  ap- 
peared in  the  constellation  Cygnus,  and  attained  at 
one  time  the  brightness  of  the  second  magnitude. 



Its  spectrum  and  its  behavior  resembled  those  of  its 
immediate  predecessor.  In  1885  astronomers  were 
surprised  to  see  a  sixth-magnitude  star  glimmering 
in  the  midst  of  the  hazy  cloud  of  the  great  Andromeda 
Nebula.  It  soon  absolutely  disappeared.  Its  spec- 
trum was  remarkable  for  being  "continuous,"  like 
that  of  the  nebula  itself.  A  continuous  spectrum  is 
supposed  to  represent  a  body,  or  a  mass,  which  is 
either  solid  or  liquid,  or  composed  of  gas  under  great 
pressure.  In  January,  1892,  a  new  star  was  suddenly 
seen  in  the  constellation  Auriga.  It  never  rose  much 
above  the  fourth  magnitude,  but  it  showed  a  peculiar 
spectrum  containing  both  bright  and  dark  lines  of 

But  a  bewildering  surprise  was  now  in  store;  the 
world  was  to  behold  at  the  opening  of  the  twentieth 
century  such  a  celestial  spectacle  as  had  not  been  on 
view  since  the  times  of  Tycho  and  Kepler.  Before 
daylight  on  the  morning  of  February  22,  1901,  the 
Rev.  Doctor  Anderson,  of  Edinburgh,  an  amateur 
astronomer,  who  had  also  been  the  first  to  see  the  new 
star  in  Auriga,  beheld  a  strange  object  in  the  con- 
stellation Perseus  not  far  from  the  celebrated  variable 
star  Algol.  He  recognized  its  character  at  once,  and 
immediately  telegraphed  the  news,  which  awoke  the 
startled  attention  of  astronomers  all  over  the  world. 
When  first  seen  the  new  star  was  no  brighter  than 
Algol  (less  than  the  second  magnitude),  but  within 
twenty-four  hours  it  was  ablaze,  outshining  even  the 
brilliant  Capella,  and  far  surpassing  the  first  magni- 
tude. At  the  spot  in  the  sky  where  it  appeared  noth- 
ing whatever  was  visible  on  the  night  before  its  com- 



ing.  This  is  known  with  certainty  because  a  photo- 
graph had  been  made  of  that  very  region  on  Feb- 
ruary 21,  and  this  photograph  showed  everything 
down  to  the  twelfth  magnitude,  but  not  a  trace  of  the 
stranger  which  burst  into  view  between  the  2ist  and 
the  22d  like  the  explosion  of  a  rocket. 

Upon  one  who  knew  the  stars  the  apparition  of  this 
intruder  in  a  well-known  constellation  had  the  effect 
of  a  sudden  invasion.  The  new  star  was  not  far  west 
of  the  zenith  in  the  early  evening,  and  in  that  position 
showed  to  the  best  advantage.  To  see  Capella,  the 
hitherto  unchallenged  ruler  of  that  quarter  of  the 
sky,  abased  by  comparison  with  this  stranger  of  alien 
aspect,  for  there  was  always  an  unfamiliar  look  about 
the  "nova,"  was  decidedly  disconcerting.  It  seemed 
to  portend  the  beginning  of  a  revolution  in  the  heavens. 
One  could  understand  what  the  effect  of  such  an 
apparition  must  have  been  in  the  superstitious  times 
of  Tycho.  The  star  of  Tycho  had  burst  forth  on  the 
northern  border  of  the  Milky  Way;  this  one  was  on 
its  southern  border,  some  forty-five  degrees  farther 

Astronomers  were  well  prepared  this  time  for  the 
scientific  study  of  the  new  star,  both  astronomical 
photography  and  spectroscopy  having  been  perfected, 
and  the  results  of  their  investigations  were  calculated 
to  increase  the  wonder  with  which  the  phenomenon 
was  regarded.  The  star  remained  at  its  brightest 
only  a  few  days  •  then,  like  a  veritable  conflagration,  it 
began  to  languish •  and,  like  the  reflection  of  a  dying 
fire,  as  it  sank  it  began  to  glow  with  the  red  color  of 
embers.  But  its  changes  were  spasmodic ;  once  about 



every  three  days  it  flared  up  only  to  die  away  again. 
During  these  fluctuations  its  light  varied  alternately 
in  the  ratio  of  one  to  six.  Finally  it  took  a  permanent 
downward  course,  and  after  a  few  months  the  naked 
eye  could  no  longer  perceive  it;  but  it  remained 
visible  with  telescopes,  gradually  fading  until  it  had 
sunk  to  the  ninth  magnitude.  Then  another  as- 
tonishing change  happened:  in  August  photographs 
taken  at  the  Yerkes  Observatory  and  at  Heidelberg 
showed  that  the  "nova"  was  surrounded  by  a  spiral 
nebula!  The  nebula  had  not  been  there  before, 
and  no  one  could  doubt  that  it  represented  a  phase 
of  the  same  catastrophe  that  had  produced  the  out- 
burst of  the  new  star.  At  one  time  the  star  seemed 
virtually  to  have  disappeared,  as  if  all  its  substance 
had  been  expanded  into  the  nebulous  cloud,  but 
always  there  remained  a  stellar  nucleus  about  which 
the  misty  spiral  spread  wider  and  ever  wider,  like  a 
wave  expanding  around  a  centre  of  disturbance.  The 
nebula  too  showed  a  variability  of  brightness,  and  four 
condensations  which  formed  in  it  seemed  to  have  a 
motion  of  revolution  about  the  star.  As  time  went 
on  the  nebula  continued  to  expand  at  a  rate  which 
was  computed  to  be  not  less  than  twenty  thousand 
miles  per  second!  And  now  the  star  itself,  showing 
indications  of  having  turned  into  a  nebula,  behaved 
in  av  most  erratic  manner,  giving  rise  to  the  suspicion 
that  it  was  about  to  burst  out  again.  But  this  did 
not  occur,  and  at  length  it  sunk  into  a  state  of  lethargy 
from  which  it  has  to  the  present  time  not  recovered. 
But  the  nebulous  spiral  has  disappeared,  and  the 
entire  phenomenon  as  it  now  (1909)  exists  consists 



of  a  faint  nebulous  star  of  less  than  the  ninth  magni- 

The  wonderful  transformations  just  described  had 
been  forecast  in  advance  of  the  discovery  of  the 
nebulous  spiral  encircling  the  star  by  the  spectro- 
scopic  study  of  the  latter.  At  first  there  was  no  sug- 
gestion of  a  nebular  constitution,  but  within  a  month 
or  two  characteristic  nebular  lines  began  to  appear, 
and  in  less  than  six  months  the  whole  spectrum  had 
been  transformed  to  the  nebular  type.  In  the  mean 
time  the  shifting  of  the  spectral  lines  indicated  a  com- 
plication of  rapid  motions  in  several  directions  simul- 
taneously. These  motions  were  estimated  to  amount 
to  from  one  hundred  to  five  hundred  miles  per  second. 

The  human  mind  is  so  constituted  that  it  feels 
forced  to  seek  an  explanation  of  so  marvellous  a 
phenomenon  as  this,  even  in  the  absence  of  the  data 
needed  for  a  sound  conclusion.  The  most  natural 
hypothesis,  perhaps,  is  that  of  a  collision.  Such  a 
catastrophe  could  certainly  happen.  It  has  been 
shown,  for  instance,  that  in  infinity  of  time  the  earth 
is  sure  to  be  hit  by  a  comet ;  in  the  same  way  it  may 
be  asserted  that,  if  no  time  limit  is  fixed,  the  sun  is 
certain  to  run  against  some  obstacle  in  space,  either 
another  star,  or  a  dense  meteor  swarm,  or  one  of  the 
dark  bodies  which  there  is  every  reason  to  believe 
abound  around  us.  The  consequences  of  such  a 
collision  are  easy  to  foretell,  provided  that  we  know 
the  masses  and  the  velocities  of  the  colliding  bodies. 
In  a  preceding  chapter  we  have  discussed  the  motions 
of  the  sun  and  stars,  and  have  seen  that  they  are  so 
swift  that  an  encounter  between  any  two  of  them 


could  not  but  be  disastrous.  But  this  is  not  all; 
for  as  soon  as  two  stars  approached  within  a  few 
million  miles  their  speed  would  be  enormously  in- 
creased by  their  reciprocal  attractions  and,  if  their 
motion  was  directed  radially  with  respect  to  their 
centres,  they  would  come  together  with  a  crash  that 
would  reduce  them  both  to  nebulous  clouds.  It  is 
true  that  the  chances  of  such  a  "head-on*'  collision 
are  relatively  very  small;  two  stars  approaching  each 
other  would  most  probably  fall  into  closed  orbits 
around  their  common  centre  of  gravity.  If  there 
were  a  collision  it  would  most  likely  be  a  grazing  one 
instead  of  a  direct  front-to-front  encounter.  But 
even  a  close  approach,  without  any  actual  collision, 
would  probably  prove  disastrous,  owing  to  the  tidal 
influence  of  each  of  the  bodies  upon  the  other.  Suns, 
in  consequence  of  their  enormous  masses  and  di- 
mensions and  the  peculiarities  of  their  constitution, 
are  exceedingly  dangerous  to  one  another  at  close 
quarters.  Propinquity  awakes  in  them  a  mutually 
destructive  tendency.  Consisting  of  matter  in  the 
gaseous,  or  perhaps,  in  some  cases,  liquid,  state,  their 
tidal  pull  upon  each  other  if  brought  close  together 
might  burst  them  asunder,  and  the  photospheric 
envelope  being  destroyed  the  internal  incandescent 
mass  would  gush  out,  bringing  fiery  death  to  any 
planets  that  were  revolving  near.  Without  regard 
to  the  resulting  disturbance  of  the  earth's  orbit,  the 
close  approach  of  a  great  star  to  the  sun  would  be  in 
the  highest  degree  perilous  to  us.  But  this  is  a  danger 
which  may  properly  be  regarded  as  indefinitely  re- 
mote, since,  at  our  present  location  in  space,  we  are 



certainly  far  from  every  star  except  the  sun,  and  we 
may  feel  confident  that  no  great  invisible  body  is 
near,  for  if  there  were  one  we  should  be  aware  of  its 
presence  from  the  effects  of  its  attraction.  As  to 
dark  nebulae  which  may  possibly  lie  in  the  track  that 
the  solar  system  is  pursuing  at  the  rate  of  375,000,000 
miles  per  year,  that  is  another  question — and  they,  too, 
could  be  dangerous! 

This  brings  us  directly  back  to  "Nova  Persi,"  for 
among  the  many  suggestions  offered  to  explain  its 
outburst,  as  well  as  those  of  other  temporary  stars, 
one  of  the  most  fruitful  is  that  of  a  collision  between 
a  star  and  a  vast  invisible  nebula.  Professor  Seeliger, 
of  Munich,  first  proposed  this  theory,  but  it  afterward 
underwent  some  modifications  from  others.  Stated 
in  a  general  form,  the  idea  is  that  a  huge  dark  body, 
perhaps  an  extinguished  sun,  encountered  in  its 
progress  through  space  a  widespread  flock  of  small 
meteors  forming  a  dark  nebula.  As  it  plunged  into 
the  swarm  the  friction  of  the  innumerable  collisions 
with  the  meteors  heated  its  surface  to  incandescence, 
and  being  of  vast  size  it  then  became  visible  to  us  as  a 
new  star.  Meanwhile  the  motion  of  the  body  through 
the  nebula,  and  its  rotation  upon  itself,  set  up  a 
gyration  in  the  blazing  atmosphere  formed  around  it 
by  the  vaporized  meteors;  and  as  this  atmosphere 
spread  wider,  under  the  laws  of  gyratory  motion  a 
rotation  in  the  opposite  direction  began  in  the  in- 
flamed meteoric  cloud  outside  the  central  part  of  the 
vortex.  Thus  the  spectral  lines  were  caused  to  show 
motion  in  opposite  directions,  a  part  of  the  incan- 
descent mass  approaching  the  earth  simultaneously 



with  the  retreat  of  another  part.  So  the  curious 
spectroscopic  observations  before  mentioned  were  ex- 
plained. This  theory  might  also  account  for  the 
appearance  of  the  nebulous  spiral  first  seen  some  six 
months  after  the  original  outburst.  The  sequent 
changes  in  the  spectrum  of  the  "nova"  are  accounted 
for  by  this  theory  on  the  assumption,  reasonable 
enough  in  itself,  that  at  first  the  invading  body  would 
be  enveloped  in  a  vaporized  atmosphere  of  relatively 
slight  depth,  producing  by  its  absorption  the  fine 
dark  lines  first  observed*  but  that  as  time  went  on 
and  the  incessant  collisions  continued,  the  blazing 
atmosphere  would  become  very  deep  and  extensive, 
whereupon  the  appearance  of  the  spectral  lines  would 
change,  and  bright  lines  due  to  the  light  of  the  in- 
candescent meteors  surrounding  the  nucleus  at  a 
great  distance  would  take  the  place  of  the  original 
dark  ones.  The  vortex  of  meteors  once  formed 
would  protect  the  flying  body  within  from  further 
immediate  collisions,  the  latter  now  occurring  mainly 
among  the  meteors  themselves,  and  then  the  central 
blaze  would  die  down,  and  the  original  splendor  of  the 
phenomenon  would  fade. 

But  the  theories  about  Nova  Persei  have  been 
almost  as  numerous  as  the  astronomers  who  have 
speculated  about  it.  One  of  the  most  startling  of 
them  assumed  that  the  outburst  was  caused  by  the 
running  amuck  of  a  dark  star  which  had  encountered 
another  star  surrounded  with  planets,  the  renewed 
outbreaks  of  light  after  the  principal  one  had  faded 
being  due  to  the  successive  running  down  of  the  un- 
fortunate planets!  Yet  another  hypothesis  is  based 



on  what  we  have  already  said  of  the  tidal  influence 
that  two  close  approaching  suns  would  have  upon 
each  other.  Supposing  two  such  bodies  which  had 
become  encrusted,  but  remained  incandescent  and 
fluid  within,  to  approach  within  almost  striking  dis- 
tance; they  would  whirl  each  other  about  their  com- 
mon centre  of  gravity,  and  at  the  same  time  their 
shells  would  burst  under  the  tidal  strain,  and  their 
glowing  nuclei  being  disclosed  would  produce  a  great 
outburst  of  light.  Applying  this  theory  to  a  "nova/* 
like  that  of  1866  in  the  "Northern  Crown,"  which 
had  been  visible  as  a  small  star  before  the  outbreak, 
and  which  afterward  resumed  its  former  aspect,  we 
should  have  to  assume  that  a  yet  shining  sun  had 
been  approached  by  a  dark  body  whose  attraction 
temporarily  burst  open  its  photosphere.  It  might 
be  supposed  that  in  this  case  the  dark  body  was  too 
far  advanced  in  cooling  to  suffer  the  same  fate  from 
the  tidal  pull  of  its  victim.  But  a  close  approach  of 
that  kind  would  be  expected  to  result  in  the  forma- 
tion of  a  binary  system,  with  orbits  of  great  eccentri- 
city, perhaps,  and  after  the  lapse  of  a  certain  time  the 
outburst  should  be  renewed  by  another  approxima- 
tion of  the  two  bodies.  A  temporary  star  of  that 
kind  would  rather  be  ranked  as  a  variable. 

The  celebrated  French  astronomer,  Janssen,  had  a 
different  theory  of  Nova  Persei,  and  of  temporary 
stars  in  general.  According  to  his  idea,  such  phe- 
nomena might  be  the  result  of  chemical  changes 
taking  place  in  a  sun  without  interference  by,  or 
collision  with,  another  body.  Janssen  was  engaged 
for  many  years  in  trying  to  discover  evidence  of  the 



existence  of  oxygen  in  the  sun,  and  he  constructed  his 
observatory  on  the  summit  of  Mont  Blanc  specially 
to  pursue  that  research.  He  believed  that  oxygen 
must  surely  exist  in  the  sun  since  we  find  so  many  other 
familiar  elements  included  in  the  constitution  of  the 
solar  globe,  and  as  he  was  unable  to  discover  satis- 
factory evidence  of  its  presence  he  assumed  that  it 
existed  there  in  a  form  unknown  on  the  earth.  If 
it  were  normally  in  the  sun's  chromosphere,  or 
coronal  atmosphere,  he  said,  it  would  combine  with 
the  hydrogen  which  we  know  is  there  and  form  an 
obscuring  envelope  of  water  vapor.  It  exists,  then, 
in  a  special  state,  uncombined  with  hydrogen;  but 
let  the  temperature  of  the  sun  sink  to  a  critical  point 
and  the  oxygen  will  assume  its  normal  properties  and 
combine  with  the  hydrogen,  producing  a  mighty  out- 
burst of  light  and  heat.  This,  Janssen  thought, 
might  explain  the  phenomena  of  the  temporary  stars. 
It  would  also,  he  suggested,  account  for  their  brief 
career,  because  the  combination  of  the  elements  would 
be  quickly  accomplished,  and  then  the  resulting  water 
vapor  would  form  an  atmosphere  cutting  off  the 
radiation  from  the  star  within. 

This  theory  may  be  said  to  have  a  livelier  human 
interest  than  some  of  the  others,  since,  according  to  it, 
the  sun  may  carry  in  its  very  constitution  a  menace 
to  mankind;  one  does  not  like  to  think  of  it  being  sud- 
denly transformed  into  a  gigantic  laboratory  for  the 
explosive  combination  of  oxygen  and  hydrogen! 
But  while  Janssen' s  theory  might  do  for  some  tem- 
porary stars,  it  is  inadequate  to  explain  all  the 
phenomena  of  Nova  Persei,  and  particularly  the 



appearance  of  the  great  spiral  nebula  that  seemed  to 
exhale  from  the  heart  of  the  star.  Upon  the  whole, 
the  theory  of  an  encounter  between  a  star  and  a  dark 
nebula  seems  best  to  fit  the  observations.  By  that 
hypothesis  the  expanding  billow  of  light  surrounding 
the  core  of  the  conflagration  is  very  well  accounted 
for,  and  the  spectroscopic  peculiarities  are  also  ex- 

Dr.  Gustav  Le  Bon  offers  a  yet  more  alarming 
theory,  suggesting  that  temporary  stars  are  the 
result  of  atomic  explosion;  but  we  shall  touch  upon 
this  more  fully  in  Chapter  XIV. 

Twice  in  the  course  of  this  discussion  we  have 
called  attention  to  the  change  of  color  invariably 
undergone  by  temporary  stars  in  the  later  stages  of 
their  career.  This  was  conspicuous  with  Nova 
Persei  which  glowed  more  and  more  redly  as  it  faded, 
until  the  nebulous  light  began  to  overpower  that  of 
the  stellar  nucleus.  Nothing  could  be  more  sugges- 
tive of  the  dying  out  of  a  great  fire.  Moreover, 
change  of  color  from  white  to  red  is  characteristic  of 
all  variable  stars  of  long  period,  such  as  "Mira"  in 
Cetus.  It  is  also  characteristic  of  stars  believed  to 
be  in  the  later  stages  of  evolution,  and  consequently 
approaching  extinction,  like  Antares  and  Betelgeuse, 
and  still  more  notably  certain  small  stars  which 
"gleam  like  rubies  in  the  field  of  the  telescope." 
These  last  appear  to  be  suns  in  the  closing  period  of 
existence  as  self-luminous  bodies.  Between  the  white 
stars,  such  as  Sirius  and  Rigel,  and  the  red  stars,  such 
as  Aldebaran  and  Alpha  Herculis,  there  is  a  pro- 
gressive series  of  colors  from  golden  yellow  through 



orange  to  deep  red.  The  change  is  believed  to  be  due 
to  the  increase  of  absorbing  vapors  in  the  stellar 
atmosphere  as  the  body  cools  down.  In  the  case  of 
ordinary  stars  these  changes  no  doubt  occupy  many 
millions  of  years,  which  represent  the  average  dura- 
tion of  solar  life;  but  the  temporary  stars  run  through 
similar  changes  in  a  few  months:  they  resemble 
ephemeral  insects — born  in  the  morning  and  doomed 
to  perish  with  the  going  down  of  the  sun. 



ONE  of  the  most  surprising  triumphs  of  celestial 
photography  was  Professor  Keeler's  discovery, 
in  1899,  that  the  great  majority  of  the  nebulae  have  a 
distinctly  spiral  form.  This  form,  previously  known 
in  Lord Rosse's  great  " Whirlpool  Nebula,"  had  been 
supposed  to  be  exceptional;  now  the  photographs, 
far  excelling  telescopic  views  in  the  revelation  of 
nebular  forms,  showed  the  spiral  to  be  the  typical 
shape.  Indeed,  it  is  a  question  whether  all  nebulae  are 
not  to  some  extent  spiral.  The  extreme  importance 
of  this  discovery  is  shown  in  the  effect  that  it  has  had 
upon  hitherto  prevailing  views  of  solar  and  planetary 
evolution.  For  more  than  three-quarters  of  a  century 
Laplace's  celebrated  hypothesis  of  the  manner  of 
origin  of  the  solar  system  from  a  rotating  and  con- 
tracting nebula  surrounding  the  sun  had  guided 
speculation  on  that  subject,  and  had  been  tentatively 
extended  to  cover  the  evolution  of  systems  in  general. 
The  apparent  forms  of  some  of  the  nebulas  which  the 
telescope  had  revealed  were  regarded,  and  by  some 
are  still  regarded,  as  giving  visual  evidence  in  favor 
of  this  theory.  There  is  a  "ring  nebula"  in  Lyra 
with  a  central  star,  and  a  "planetary  nebula"  in 




Gemini  bearing  no  little  resemblance  to  the  planet 
Saturn  with  its  rings,  both  of  which  appear  to  be 
practical  realizations  of  Laplace's  idea,  and  the 
elliptical  rings  surrounding  the  central  condensation 
of  the  Andromeda  Nebula  may  be  cited  for  the  same 
kind  of  proof. 

But  since  Keeler's  discovery  there  has  been  a  de- 
cided turning  of  speculation  another  way.  The  form 
of  the  spiral  nebulae  seems  to  be  entirely  inconsistent 
with  the  theory  of  an  originally  globular  or  disk- 
shaped  nebula  condensing  around  a  sun  and  throw- 
ing or  leaving  off  rings,  to  be  subsequently  shaped 
into  planets.  Some  astronomers,  indeed,  now  reject 
Laplace's  hypothesis  in  toto,  preferring  to  think  that 
even  our  solar  system  originated  from  a  spiral  nebula. 
Since  the  spiral  type  prevails  among  the  existing 
nebulas,  we  must  make  any  mechanical  theory  of  the 
development  of  stars  and  planetary  systems  from 
them  accord  with  the  requirements  which  that  form 
imposes.  A  glance  at  the  extraordinary  variations 
upon  the  spiral  which  Professor  Keeler's  photographs 
reveal  is  sufficient  to  convince  one  of  the  difficulty 
of  the  task  of  basing  a  general  theory  upon  them.  In 
truth,  it  is  much  easier  to  criticize  Laplace's  hypothesis 
than  to  invent  a  satisfactory  substitute  for  it.  If  the 
spiral  nebulae  seem  to  oppose  it  there  are  other  nebulae 
which  appear  to  support  it,  and  it  may  be  that  no  one 
fixed  theory  can  account  for  all  the  forms  of  stellar 
evolution  in  the  universe.  Our  particular  planetary 
system  may  have  originated  very  much  as  the  great 
French  mathematician  supposed,  while  others  have 
undergone,  or  are  now  undergoing,  a  different  process 



of  development.  There  is  always  a  too  strong 
tendency  to  regard  an  important  new  discovery  and 
the  theories  and  speculations  based  upon  it  as  revolu- 
tionizing knowledge,  and  displacing  or  overthrowing 
everything  that  went  before.  Upon  the  plea  that 
''Laplace  only  made  a  guess"  more  recent  guesses 
have  been  driven  to  extremes  and  treated  by  in- 
judicious exponents  as  "the  solid  facts  at  last." 

Before  considering  more  recent  theories  than  La- 
place's, let  us  see  what  the  nature  of  the  photographic 
revelations  is.  The  vast  celestial  maelstrom  dis- 
covered by  Lord  Rosse  in  the  "Hunting  Dogs"  may 
be  taken  as  the  leading  type  of  the  spiral  nebulas, 
although  there  are  less  conspicuous  objects  of  the  kind 
which,  perhaps,  better  illustrate  some  of  their  pe- 
culiarities. Lord  Rosse's  nebula  appears  far  more 
wonderful  in  the  photographs  than  in  his  drawings 
made  with  the  aid  of  his  giant  reflecting  telescope  at 
Parsonstown,  for  the  photographic  plate  records 
details  that  no  telescope  is  capable  of  showing. 
Suppose  we  look  at  the  photograph  of  this  object  as 
any  person  of  common  sense  would  look  at  any  great 
and  strange  natural  phenomenon.  What  is  the  first 
thing  that  strikes  the  mind?  It  is  certainly  the  ap- 
pearance of  violent  whirling  motion.  One  would  say 
that  the  whole  glowing  mass  had  been  spun  about  with 
tremendous  velocity,  or  that  it  had  been  set  rotating 
so  rapidly  that  it  had  become  the  victim  of  "centrif- 
ugal force,"  one  huge  fragment  having  broken  loose 
and  started  to  gyrate  off  into  space.  Closer  inspec- 
tion shows  that  in  addition  to  the  principal  focus 
there  are  various  smaller  condensations  scattered 




through  the  mass.  These  are  conspicuous  in  the 
spirals.  Some  of  them  are  stellar  points,  and  but  for 
the  significance  of  their  location  we  might  suppose 
them  to  be  stars  which  happen  to  lie  in  line  between 
us  and  the  nebula.  But  when  we  observe  how  many 
of  them  follow  most  faithfully  the  curves  of  the 
spirals  we  cannot  but  conclude  that  they  form  an 
essential  part  of  the  phenomenon;  it  is  not  possible 
to  believe  that  their  presence  in  such  situations  is 
merely  fortuitous.  One  of  the  outer  spirals  has  at 
least  a  dozen  of  these  star-like  points  strung  upon  it; 
some  of  them  sharp,  small,  and  distinct,  others  more 
blurred  and  nebulous,  suggesting  different  stages  of 
condensation.  Even  the  part  which  seems  to  have 
been  flung  loose  from  the  main  mass  has,  in  addition 
to  its  central  condensation,  at  least  one  stellar  point 
gleaming  in  the  half-vanished  spire  attached  to 
it.  Some  of  the  more  distant  stars  scattered  around 
the  "whirlpool"  look  as  if  they  too  had  been  shot  out 
of  the  mighty  vortex,  afterward  condensing  into  un- 
mistakable solar  bodies.  There  are  at  least  two 
curved  rows  of  minute  stars  a  little  beyond  the 
periphery  of  the  luminous  whorl  which  clearly  follow 
lines  concentric  with  those  of  the  nebulous  spirals. 
Such  facts  are  simply  dumfounding  for  any  one  who 
will  bestow  sufficient  thought  upon  them,  for  these 
are  suns,  though  they  may  be  small  ones ;  and  what  a 
birth  is  that  for  a  sun! 

Look  now  again  at  the  glowing  spirals.      We  ob- 
serve that  hardly  have  they  left  the  central  mass  be- 
fore they  begin  to  coagulate.     In  some  places  they 
have  a  "ropy"  aspect;  or  they  are  like  peascods  filled 
6  95 


with  growing  seeds,  which  eventually  will  become 
stars.  The  great  focus  itself  shows  a  similar  tendency, 
especially  around  its  circumference.  The  sense  that 
it  imparts  of  a  tremendous  shattering  force  at  w^ork 
is  overwhelming.  There  is  probably  more  matter  in 
that  whirling  and  bursting  nebula  than  would  suffice 
to  make  a  hundred  solar  systems!  It  must  be  con- 
fessed at  once  that  there  is  no  confirmation  of  the 
Laplacean  hypothesis  here;  but  what  hypothesis  will 
fit  the  facts  ?  There  is  one  which  it  has  been  claimed 
does  so,  but  we  shall  come  to  that  later.  In  the 
meanwhile,  as  a  preparation,  fix  in  the  memory  the 
appearance  of  that  second  spiral  mass  spinning  be- 
side its  master  which  seems  to  have  spurned  it 

For  a  second  example  of  the  spiral  nebulas  look  at 
the  one  in  the  constellation  Triangulum.  Go d,  haw 
hath  the  imagination  of  puny  man  failed  to  comprehend 
Thee!  Here  is  creation  through  destruction  with  a 
vengeance!  The  spiral  form  of  the  nebula  is  un- 
mistakable, but  it  is  half  obliterated  amid  the  turmoil 
of  flying  masses  hurled  away  on  all  sides  with  tornadic 
fury.  The  focus  itself  is  splitting  asunder  under  the 
intolerable  strain,  and  in  a  little  while,  as  time  is 
reckoned  in  the  Cosmos,  it  will  be  gyrating  into  stars. 
And  then  look  at  the  cyclonic  rain  of  already  finished 
stars  whirling  round  the  outskirts  of  the  storm. 
Observe  how  scores  of  them  are  yet  involved  in  the 
fading  streams  of  the  nebulous  spirals;  see  how  they 
have  been  thrown  into  vast  loops  and  curves,  of  a 
beauty  that  half  redeems  the  terror  of  the  spectacle 
enclosed  within  their  lines — like  iridescent  cirri  hover- 




ing  about  the  edges  of  a  hurricane.     And  so  again 
are  suns  born! 

Let  us  turn  to  the  exquisite  spiral  in  Ursa  Major; 
how  different  its  aspect  from  that  of  the  other!  One 
would  say  that  if  the  terrific  coil  in  Triangulum  has 
all  but  destroyed  itself  in  its  fury,  this  one  on  the  con- 
trary has  just  begun  its  self-demolition.  As  one 
gazes  one  seems  to  see  in  tt  the  smooth,  swift,  accelerat- 
ing motion  that  precedes  catastrophe.  The  central 
part  is  still  intact,  dense,  and  uniform  in  texture. 
How  graceful  are  the  spirals  that  smoothly  rise  from 
its  oval  rim  and,  gemmed  with  little  stars,  wind  off 
into  the  darkness  until  they  have  become  as  delicate 
as  threads  of  gossamer!  But  at  bottom  the  story  told 
here  is  the  same — creation  by  gyration! 

Compare  with  the  above  the  curious  mass  in  Cetus. 
Here  the  plane  of  the  whirling  nebula  nearly  coincides 
with  our  line  of  sight  and  we  see  the  object  at  a  low 
angle.  It  is  far  advanced  and  torn  to  shreds,  and  if 
we  could  look  at  it  perpendicularly  to  its  plane  it  is  . 
evident  that  it  would  closely  resemble  the  spectacle 
in  Triangulum. 

Then  take  the    famous  Andromeda  Nebula   (see 
Frontispiece),  which  is  so  vast  that  notwithstanding  ; 
its  immense  distance  even  the  naked  eye  perceives  it  j 
as  an  enigmatical  wisp  in  the  sky.     Its  image  on  the  j 
sensitive  plate  is  the  masterpiece  of  astronomical  pho  j 
tography;  for  wild,  incomprehensible  beauty  there  is  j 
nothing  that  can  be  compared  with  it.     Here,  if  any-  I 
where,  we  look  upon  the  spectacle  of  creation  in  one  of 
its  earliest  stages.     The  Andromeda  Nebula  is  appar- 
ently less  advanced  toward  transformation  into  stellar 



bodies  than  is  that  in  Triangulum.  The  immense 
crowd  of  stars  sprinkled  over  it  and  its  neighborhood 
seem  in  the  main  to  lie  this  side  of  the  nebula,  and  con- 
sequently to  have  no  connection  with  it.  But  incip- 
ient stars  (in  some  places  clusters  of  them)  are  seen 
in  the  nebulous  rings,  while  one  or  two  huge  masses 
seem  to  give  promise  of  transformation  into  stellar 
bodies  of  unusual  magnitude.  I  say  "rings"  because 
although  the  loops  encompassing  the  Andromeda  Neb- 
ebula  have  been  called  spirals  by  those  who  wish  ut- 
terly to  demolish  Laplace's  hypothesis,  yet  they  are  not 
manifestly  such,  as  can  be  seen  on  comparing  them 
with  the  undoubted  spirals  of  the  Lord  Rosse  Nebula. 
They  look  quite  as  much  like  circles  or  ellipses  seen  at 
an  angle  of,  say,  fifteen  or  twenty  degrees  to  their 
plane.  If  they  are  truly  elliptical  they  accord  fairly 
well  with  Laplace's  idea,  except  that  the  scale  of 
magnitude  is  stupendous,  and  if  the  Andromeda 
Nebula  is  to  become  a  solar  system  it  will  surpass  ours 
in  grandeur  beyond  all  possibility  of  comparison. 

There  is  one  circumstance  connected  with  the  spiral 
nebulae,  and  conspicuous  in  the  Andromeda  Nebula 
on  account  of  its  brightness,  which  makes  the  ques- 
tion of  their  origin  still  more  puzzling ;  they  all  show 
continuous  spectra,  which,  as  we  have  before  remarked, 
indicate  that  the  mass  from  which  the  light  comes  is 
either  solid  or  liquid,  or  a  gas  under  heavy  pressure. 
Thus  nebulae  fall  into  two  classes:  the  "white" 
nebulae,  giving  a  continuous  spectrum;  and  the 
"green"  nebulas  whose  spectra  are  distinctly  gaseous. 
The  Andromeda  Nebula  is  the  great  representative 
of  the  former  class  and  the  Orion  Nebula  of  the  latter. 




The  spectrum  of  the  Andromeda  Nebula  has  been 
interpreted  to  mean  that  it  consists  not  of  luminous 
gas,  but  of  a  flock  of  stars  so  distant  that  they  are 
separately  indistinguishable  even  with  powerful  tele- 
scopes, just  as  the  component  stars  of  the  Milky  Way 
are  indistinguishable  with  the  naked  eye;  and  upon 
this  has  been  based  the  suggestion  that  what  we  see 
in  Andromeda  is  an  outer  universe  whose  stars  form 
a  series  of  elliptical  garlands  surrounding  a  central 
mass  of  amazing  richness.  But  this  idea  is  unac- 
ceptable if  for  no  other  reason  than  that,  as  just  said, 
all  the  spiral  nebulas  possess  the  same  kind  of  spec- 
trum, and  probably  no  one  would  be  disposed  to  re- 
gard them  all  as  outer  universes.  As  we  shall  see  later, 
the  peculiarity  of  the  spectra  of  the  spiral  nebulas  is 
appealed  to  in  support  of  a  modern  substitute  for 
Laplace's  hypothesis. 

Finally,  without  having  by  any  means  exhausted 
the  variety  exhibited  by  the  spiral  nebulae,  let  us 
turn  to  the  great  representative  of  the  other  species, 
the  Ori^2_J^ebula.  In  some  ways  this  is  even  more 
marvellous  thaiTthe  others.  The  early  drawings  with 
the  telescope  failed  to  convey  an  adequate  con- 
ception either  of  its  sublimity  or  of  its  complication 
of  structure.  It  exists  in  a  nebulous  region  of  space, 
since  photographs  show  that  nearly  the  whole  con- 
stellation is  interwoven  with  faintly  luminous  coils. 
To  behold  the  entry  of  the  great  nebula  into  the  field 
even  of  a  small  telescope  is  a  startling  experience  which 
never  loses  its  novelty.  As  shown  by  the  photo- 
graphs, it  is  an  inscrutable  chaos  of  perfectly  amazing 
extent,  where  spiral  bands,  radiating  streaks,  dense 



masses,  and  dark  yawning  gaps  are  strangely  inter- 
mingled without  apparent  order.  In  one  place  four 
conspicuous  little  stars,  better  seen  with  a  telescope 
than  in  the  photograph  on  account  of  the  blurring 
produced  by  over-exposure,  are  suggestively  situated 
in  the  midst  of  a  dark  opening,  and  no  observer  has 
ever  felt  any  doubt  that  these  stars  have  been  formed 
from  the  substance  of  the  surrounding  nebula.  There 
are  many  other  stars  scattered  over  its  expanse  which 
manifestly  owe  their  origin  to  the  same  source.  But 
compare  the  general  appearance  of  this  nebula  with 
the  others  that  we  have  studied,  and  remark  the  dif- 
ference. If  the  unmistakably  spiral  nebulae  resemble 
bursting  fly-wheels  or  grindstones  from  whose  perim- 
eters torrents  of  sparks  are  flying,  the  Orion  Nebula 
rather  recalls  the  aspect  of  a  cloud  of  smoke  and 
fragments  produced  by  the  explosion  of  a  shell.  This 
idea  is  enforced  by  the  look  of  the  outer  portion  far- 
thest from  the  bright  half  of  the  nebula,  where  sharply 
edged  clouds  with  dark  spaces  behind  seem  to  be 
billowing  away  as  if  driven  by  a  wind  blowing  from 
the  centre. 

Next  let  us  consider  what  scientific  speculation  has 
done  in  the  effort  to  explain  these  mysteries.  La- 
place's hypothesis  can  certainly  find  no  standing 
ground  either  in  the  Orion  Nebula  or  in  those  of  a 
spiral  configuration,  whatever  may  be  its  situation 
with  respect  to  the  grand  Nebula  of  Andromeda,  or 
the  "ring'*  and  "planetary"  nebulas.  Some  other 
hypothesis  more  consonant  with  the  appearances 
must  be  found.  Among  the  many  that  have  been 
proposed  the  most  elaborate  is  the  "  PlanetesimaJ 




Hypothesis"  of  Professors  Chamberlin  and  Moulton. 
It  is  to  be  remarked  that  it  applies  to  the  spiral 
nebulae  distinctively,  and  not  to  an  apparently  chaotic 
mass  of  gas  like  the  vast  luminous  cloud  in  Orion. 
The  gist  of  the  theory  is  that  these  curious  objects 
are  probably  the  result  of  close  approaches  to  each 
other  of  two  independent  suns,  reminding  us  of  what 
was  said  on  this  subject  when  we  were  dealing  with 
temporary  stars.  Of  the  previous  history  of  these 
appulsing  suns  the  theory  gives  us  no  account ;  they  are 
simply  supposed  to  arrive  within  what  may  be  called 
an  effective  tide-producing  distance,  and  then  the 
drama  begins.  Some  of  the  probable  consequences 
of  such  an  approach  have  been  noticed  in  Chapter  V; 
let  us  now  consider  them  a  little  more  in  detail. 

Tides  always  go  in  couples ;  if  there  is  a  tide  on  one 
side  of  a  globe  there  will  be  a  corresponding  tide  on* 
the  other  side.  The  cause  is  to  be  found  in  the  law 
that  the  force  of  gravitation  varies  inversely  as  the 
square  of  the  distance;  the  attraction  on  the  nearest 
surface  of  a  body  exercised  by  another  body  -is 
greater  than  on  its  centre,  and  greater  yet  than  on  its 
opposite  surface.  If  two  great  globes  attract  each 
other,  each  tends  to  draw  the  other  out  into  an 
ellipsoidal  figure;  they  must  be  more  rigid  than  steel 
to  resist  this — and  even  then  they  cannot  altogether 
resist.  If  they  are  liquid  or  gaseous  they  will  yield 
readily  to  the  force  of  distortion,  the  amount  of  which 
will  depend  upon  their  distance  apart,  for  the  nearer 
they  are  the  greater  becomes  the  tidal  strain.  If 
they  are  encrusted  without  and  liquid  or  gaseous  in 
the  interior,  the  internal  mass  will  strive  to  assume 



the  figure  demanded  by  the  tidal  force,  and  will,  if  it 
can,  burst  the  restraining  envelope.  Now  this  is 
virtually  the  predicament  of  the  body  we  call  a  sun 
when  in  the  immediate  presence  of  another  body  of 
similarly  great  mass.  Such  a  body  is  presumably 
gaseous  throughout,  the  component  gases  being  held 
in  a  state  of  rigidity  by  the  compression  produced  by 
the  tremendous  gravitational  force  of  their  own 
aggregate  mass.  At  the  surface  such  a  body  is  en- 
veloped in  a  shell  of  relatively  cool  matter.  Now 
suppose  a  great  attracting  body,  such  as  another  sun, 
to  approach  near  enough  for  the  difference  in  its 
attraction  on  the  two  opposite  sides  of  the  body 
and  on  its  centre  to  become  very  great;  the  conse- 
quence will  be  a  tidal  deformation  of  the  whole  body, 
and  it  will  lengthen  out  along  the  line  of  the  gravita- 
tional pull  and  draw  in  at  the  sides,  and  if  its  shell 
offers  considerable  resistance,  but  not  enough  to 
exercise  a  complete  restraint,  it  will  be  violently  burst 
apart,  or  blown  to  atoms,  and  the  internal  mass  will 
leap  out  on  the  two  opposite  sides  in  great  fiery 
spouts.  In  the  case  of  a  sun  further  advanced  in 
cooling  than  ours  the  interior  might  be  composed  of 
molten  matter  while  the  exterior  crust  had  become 
rigid  like  the  shell  of  an  egg;  then  the  force  of  the 
"tidal  explosion"  produced  by  the  appulse  of  another 
sun  would  be  more  violent  in  consequence  of  the 
greater  resistance  overcome.  Such,  then,  is  the 
mechanism  of  the  first  phase  in  the  history  of  a  spiral 
nebula  according  to  the  Planetesimal  Hypothesis. 
Two  suns,  perhaps  extinguished  ones,  have  drawn  near 
together,  and  an  explosive  outburst  has  occurred  in 



one  or  both.  The  second  phase  calls  for  a  more  agile 
exercise  of  the  imagination. 

To  simplify  the  case,  let  us  suppose  that  only  one 
of  the  tugging  suns  is  seriously  affected  by  the  strain. 
Its  vast  wings  produced  by  the  outburst  are  twisted 
into  spirals  by  their  rotation  and  the  contending 
attractions  exercised  upon  them,  as  the  two  suns,  like 
battleships  in  desperate  conflict,  curve  round  each 
other,  concentrating  their  destructive  energies.  Then 
immense  quantities  of  debris  are  scattered  about  in 
which  eddies  are  created,  and  finally,  as  the  sun  that 
caused  the  damage  goes  on  its  way,  leaving  its  victim 
to  repair  its  injuries  as  it  may,  the  dispersed  matter 
cools,  condenses,  and  turns  into  streams  of  solid 
particles  circling  in  elliptical  paths  about  their  parent 
sun.  These  particles,  or  fragments,  are  the  "plane- 
tesimals"  of  the  theory.  In  consequence  of  the  in- 
evitable intersection  of  the  orbits  of  the  planetesimals, 
nodes  are  formed  where  the  flying  particles  meet,  and 
at  these  nodes  large  masses  are  gradually  accumulated. 
The  larger  the  mass  the  greater  its  attraction,  and  at 
last  the  nodal  points  become  the  nuclei  of  great 
aggregations  from  which  planets  are  shaped. 

This,  in  very  brief  form,  is  the  Planetesimal  Hypoth- 
esis which  we  are  asked  to  substitute  for  that  based 
on  Laplace's  suggestion  as  an  explanation  of  the  mode 
of  origin  of  the  solar  system;  and  the  phenomena  of 
the  spiral  nebulae  are  appealed  to  as  offering  evident 
support  to  the  new  hypothesis.  We  are  reminded 
that  they  are  elliptical  in  outline,  which  accords  with 
the  hypothesis;  that  their  spectra  are  not  gaseous, 
which  shows  that  they  may  be  composed  of  soli4 



particles  like  the  plahetesimals ;  and  that  their  central 
masses  present  an  oval  form,  which  is  what  would 
result  from  the  tidal  effects,  as  just  described.  We 
also  remember  that  some  of  them,  like  the  Lord  Rosse 
and  the  Andromeda  nebulae,  are  visually  double,  and 
in  these  cases  we  might  suppose  that  the  two  masses 
represent  the  tide-burst  suns  that  ventured  into  too 
close  proximity.  It  may  be  added  that  the  authors 
of  the  theory  do  not  insist  upon  the  appulse  of  two 
suns  as  the  only  way  in  which  the  planetesimals  may 
have  originated,  but  it  is  the  only  supposition  that 
has  been  worked  out. 

But  serious  questions  remain.  It  needs,  for  instance, 
but  a  glance  at  the  Triangulum  monster  to  convince 
the  observer  that  it  cannot  be  a  solar  system  which 
is  being  evolved  there,  but  rather  a  swarm  of  stars. 
Many  of  the  detached  masses  are  too  vast  to  admit 
of  the  supposition  that  they  are  to  be  transformed 
into  planets,  in  our  sense  of  planets,  and  the  distances 
of  the  stars  which  appear  to  have  been  originally 
ejected  from  the  focal  masses  are  too  great  to  allow 
us  to  liken  the  assemblage  that  they  form  to  a  solar 
system.  Then,  too,  no  nodes  such  as  the  hypothesis 
calls  for  are  visible.  Moreover,  in  most  of  the  spiral 
nebulas  the  appearances  favor  the  view  that  the 
supposititious  encountering  suns  have  not  separated 
and  gone  each  rejoicing  on  its  way,  after  having  in- 
flicted the  maximum  possible  damage  on  its  opponent, 
but  that,  on  the  contrary,  they  remain  in  close  associa- 
tion like  two  wrestlers  who  cannot  escape  from  each 
other's  grasp.  And  this  is  exactly  what  the  law  of 
gravitation  demands;  stars  cannot  approach  one 



another  with  impunity,  with  regard  either  to  their 
physical  make-up  or  their  future  independence  of 
movement.  The  theory  undertakes  to  avoid  this 
difficulty  by  assuming  that  in  the  case  of  our  system 
the  approach  of  the  foreign  body  to  the  sun  was  not  a 
close  one — just  close  enough  to  produce  the  tidal  ex- 
trusion of  the  relatively  insignificant  quantity  of 
matter  needed  to  form  the  planets.  But  even  then 
the  effect  of  the  appulse  would  be  to  change  the 
direction  of  flight,  both  of  the  sun  and  of  its  visitor, 
and  there  is  no  known  star  in  the  sky  which  can  be 
selected  as  the  sun's  probable  partner  in  their  ancient 
pas  deux.  That  there  are  unconquered  difficulties 
in  Laplace's  hypothesis  no  one  would  deny,  but  in 
simplicity  of  conception  it  is  incomparably  more 
satisfactory,  and  with  proper  modifications  could 
probably  be  made  more  consonant  with  existing  facts 
in  our  solar  system  than  that  which  is  offered  to  re- 
place it.  Even  as  an  explanation  of  the  spiral  nebulae, 
not  as  solar  systems  in  process  of  formation,  but  as  the 
birthplaces  of  stellar  clusters,  the  Planetesimal 
Hypothesis  would  be  open  to  many  objections.  Grant- 
ing its  assumptions,  it  has  undoubtedly  a  strong  math- 
ematical framework,  but  the  trouble  is  not  with  the 
mathematics  but  with  the  assumptions.  Laplace 
was  one  of  the  ablest  mathematicians  that  ever 
lived,  but  he  had  never  seen  a  spiral  nebula;  if  he 
had,  he  might  have  invented  a  hypothesis  to  suit  its 
phenomena.  His  actual  hypothesis  was  intended 
only  for  our  solar  system,  and  he  left  it  in  the  form  of 
a  "note"  for  the  consideration  of  his  successors,  with 
the  hope  that  they  might  be  able  to  discover  the  full 



truth,  which  he  confessed  was  hidden  from  him.  It 
cannot  be  said  that  that  truth  has  yet  been  found, 
and  when  it  is  found  the  chances  are  that  intuition 
and  not  logic  will  have  led  to  it. 

The  spiral  nebulae,  then,  remain  among  the  greatest 
riddles  of  the  universe,  while  the  gaseous  nebulas, 
like  that  of  Orion,  are  no  less  mysterious,  although  it 
seems  impossible  to  doubt  that  both  forms  give  birth 
to  stars.  It  is  but  natural  to  look  to  them  for  light 
on  the  question  of  the  origin  of  our  planetary  system ; 
but  we  should  not  forget  that  the  scale  of  the  phe- 
nomena in  the  two  cases  is  vastly  different,  and  the 
forces  in  operation  may  be  equally  different.  A  hill 
may  have  been  built  up  by  a  glacier,  while  a  mountain 
may  be  the  product  of  volcanic  forces  or  of  the  up- 
heaval of  the  strata  of  the  planet. 



A 5  all  the  world  knows  the  sun,  it  is  a  blinding 
globe,  pouring  forth  an  inconceivable  quantity 
of  light  and  heat,  whose  daily  passage  through  the 
sky,  caused  by  the  earth's  rotation  on  its  axis,  con- 
stitutes the  most  important  phenomenon  of  terrestrial 
existence.  Viewed  with  a  dark  glass  to  take  off  the 
glare,  or  with  a  telescope,  its  rim  is  seen  to  be  a  sharp 
and  smooth  circle,  and  nothing  but  dark  sky  is  visible 
around  it.  Except  for  the  interference  of  the  moon, 
we  should  probably  never  have  known  that  there  is 
any  more  of  the  sun  than  our  eyes  ordinarily  see. 

But  when  an  eclipse  of  the  sun  occurs,  caused  by 
the  interposition  of  the  opaque  globe  of  the  moon, 
we  see  its  immediate  surroundings,  which  in  some 
respects  are  more  wonderful  than  the  glowing  central 
orb.  These  surroundings,  although  not  in  the  sense 
in  which  we  apply  the  term  to  the  gaseous  envelope 
of  the  earth,  may  be  called  the  sun's  atmosphere. 
They  consist  of  two  very  different  parts — first,  the 
red  "prominences,"  which  resemble  tongues  of  flame 
ascending  thousands  of  miles  above  the  sun's  surface ; 
and,  second,  the  "corona,"  which  extends  to  distances 
of  millions  of  miles  from  the  sun,  and  shines  with  a 


soft,  glowing  light.  The  two  combined,  when  well  seen, 
make  a  spectacle  without  parallel  among  the  marvels 
of  the  sky.  Although  many  attempts  have  been  made 
to  render  the  corona  visible  when  there  is  no  eclipse, 
all  have  failed,  and  it  is  to  the  moon  alone  that  we  owe 
its  revelation.  To  cover  the  sun's  disk  with  a  cir- 
cular screen  will  not  answer  the  purpose  because  of 
the  illumination  of  the  air  all  about  the  observer. 
When  the  moon  hides  the  sun,  on  the  other  hand, 
the  sunlight  is  withdrawn  from  a  great  cylinder  of  air 
extending  to  the  top  of  the  atmosphere  and  spreading 
many  miles  around  the  observer.  There  is  then  no 
glare  to  interfere  with  the  spectacle,  and  the  corona 
appears  in  all  its  surprising  beauty.  The  prominences, 
however,  although  they  were  discovered  during  an 
eclipse,  can  now,  with  the  aid  of  the  spectroscope,  be 
seen  f<  t  any  time.  But  the  prominences  are  rarely 
large  enough  to  be  noticed  by  the  naked  eye,  while 
the  streamers  of  the  corona,  stretching  far  away  in 
space,  like  ghostly  banners  blown  out  from  the  black 
circle  of  the  obscuring  moon,  attract  every  eye,  and 
to  this  weird  apparition  much  of  the  fear  inspired 
by  eclipses  has  been  due.  But  if  the  corona  has  been 
a  cause  of  terror  in  the  past  it  has  become  a  source  of 
growing  knowledge  in  our  time. 

The  story  of  the  first  scientific  observation  of  the 
corona  and  the  prominences  is  thrillingly  interesting, 
and  in  fact  dramatic.  The  observation  was  made 
during  the  eclipse  of  1842,  which  fortunately  was 
visible  all  over  Central  and  Southern  Europe  so  that 
scores  of  astronomers  saw  it.  The  interest  centres 
in  what  happened  at  Pavia  in  Northern  Italy,  where 




the  English  astronomer  Francis  Baily  had  set  up  his 
telescope.  The  eclipse  had  begun  and  Baily  was  busy 
at  his  telescope  when,  to  quote  his  own  words  in  the 
account  which  he  wrote  for  the  Memoirs  of  the  Royal 
Astronomical  Society:  "I  was  astounded  by  a  tre- 
mendous burst  of  applause  from  the  streets  below, 
and  at  the  same  moment  was  electrified  by  the  sight 
of  one  of  the  most  brilliant  and  splendid  phenomena 
that  can  well  be  imagined;  for  at  that  instant  the 
dark  body  of  the  moon  was  suddenly  surrounded  with 
a  corona,  or  kind  of  bright  glory,  similar  in  shape  and 
magnitude  to  that  which  painters  draw  round  the 
heads  of  saints.  .  .  .  Pa  via  contains  many  thousand 
inhabitants,  the  major  part  of  whom  were  at  this 
early  hour  walking  about  the  streets  and  squares  or 
looking  out  of  windows  in  order  to  witness  this  long- 
talked-of  phenomenon;  and  when  the  total  obscura- 
tion took  place,  which  was  instantaneous,  there  was  a 
universal  shout  from  every  observer  which  'made 
the  welkin  ring,'  and  for  the  moment  withdrew  my 
attention  from  the  object  with  which  I  was  imme- 
diately occupied.  I  had,  indeed,  expected  the  ap- 
pearance of  a  luminous  circle  round  the  moon  during 
the  time  of  total  obscurity;  but  I  did  not  expect, 
from  any  of  the  accounts  of  preceding  eclipses  that  I 
had  read,  to  witness  so  magnificent  an  exhibition  as 
that  which  took  place.  .  .  .  Splendid  and  astonishing, 
however,  as  this  remarkable  phenomenon  really  was, 
and  although  it  could  not  fail  to  call  forth  the  admira- 
tion and  applause  of  every  beholder,  yet  I  must  con- 
fess that  there  was  at  the  same  time  something  in  its 
singular  and  wonderful  appearance  that  was  appalling. 



.  .  .  But  the  most  remarkable  circumstance  attending 
the  phenomenon  was  the  appearance  of  three  large 
protuberances  apparently  emanating  from  the  circum- 
ference of  the  moon,  but  evidently  forming  a  portion 
of  the  corona.  They  had  the  appearance  of  moun- 
tains of  a  prodigious  elevation;  their  color  was  red 
tinged  with  lilac  or  purple ;  perhaps  the  color  of  the 
peach-blossom  would  more  nearly  represent  it.  They 
somewhat  resembled  the  tops  of  the  snowy  Alpine 
mountains  when  colored  by  the  rising  or  the  setting 
sun.  They  resembled  the  Alpine  mountains  also  in 
another  respect,  inasmuch  as  their  light  was  perfectly 
steady,  and  had  none  of  that  flickering  or  sparkling 
motion  so  visible  in  other  parts  of  the  corona.  .  .  . 
The  whole  of  these  protuberances  were  visible  even 
to  the  last  moment  of  total  obscuration,  and  when 
the  first  ray  of  light  was  admitted  from  the  sun  they 
vanished,  with  the  corona,  altogether,  and  daylight 
was  instantly  restored." 

I  have  quoted  nearly  all  of  this  remarkable  descrip- 
tion not  alone  for  its  intrinsic  interest,  but  because 
it  is  the  best  depiction  that  can  be  found  of  the  general 
phenomena  of  a  total  solar  eclipse.  Still,  not  every 
such  eclipse  offers  an  equally  magnificent  spectacle. 
The  eclipses  of  1900  and  1905,  for  instance,  which 
were  seen  by  the  writer,  the  first  in  South  Carolina  and 
the  second  in  Spain,  fell  far  short  of  that  described 
by  Baily  in  splendor  and  impressiveness.  Of  course, 
something  must  be  allowed  for  the  effect  of  surprise; 
Baily  had  not  expected  to  see  what  was  so  suddenly 
disclosed  to  him.  But  both  in  1900  and  1905  the 
amount  of  scattered  light  in  the  sky  was  sufficient  in 



itself  to  make  the  corona  appear  faint,  and  there  were 
no  very  conspicuous  prominences  visible.  Yet  on 
both  occasions  there  was  manifest  among  the  specta- 
tors that  mingling  of  admiration  and  awe  of  which 
Baily  speaks.  The  South  Carolinians  gave  a  cheer 
and  the  ladies  waved  their  handkerchiefs  when  the 
corona,  ineffably  delicate  of  form  and  texture,  melted 
into  sight  and  then  in  two  minutes  melted  away 
again.  The  Spaniards,  crowded  on  the  citadel  hill 
of  Burgos,  with  their  king  and  his  royal  retinue  in 
their  midst,  broke  out  with  a  great  clapping  of  hands 
as  the  awaited  spectacle  unfolded  itself  in  the  sky; 
and  on  both  occasions,  before  the  applause  began, 
after  an  awed  silence  a  low  murmur  ran  through  the 
crowds.  At  Burgos  it  is  said  many  made  the  sign  of 
the  cross. 

It  was  not  long  before  Baily's  idea  that  the  promi- 
nences were  a  part  of  the  corona  was  abandoned,  and 
it  was  perceived  that  the  two  phenomena  were  to  a 
great  extent  independent.  At  the  eclipse  of  1868, 
which  the  astronomers,  aroused  by  the  wonderful 
scene  of  1842,  and  eager  to  test  the  powers  of  the 
newly  invented  spectroscope,  flocked  to  India  to 
witness,  Janssen  conceived  the  idea  of  employing  the 
spectroscope  to  render  the  prominences  visible  when 
there  was  no  eclipse.  He  succeeded  the  very  next 
day,  and  these  phenomena  have  been  studied  in  that 
way  ever  since. 

There  are  recognized  two  kinds  of  prominences — 
the  "eruptive"  and  the  "quiescent."  The  latter, 
which  are  cloud-like  in  form,  may  be  seen  almost  any- 
where along  the  edge  of  the  sun;  but  the  former, 
7  119 


which  often  shoot  up  as  if  hurled  from  mighty  vol- 
canoes, appear  to  be  associated  with  sun-spots,  and 
appear  only  above  the  zones  where  spots  abound. 
Either  of  them,  when  seen  in  projection  against  the 
brilliant  solar  disk,  appears  white,  not  red,  as  against 
a  background  of  sky.  The  quiescent  prominences, 
whose  elevation  is  often  from  forty  thousand  to  sixty 
thousand  miles,  consist,  as  the  spectroscope  shows, 
mainly  of  hydrogen  and  helium.  The  latter,  it  will  be 
remembered,  is  an  element  which  was  known  to  be  in 
the  sun  many  years  before  the  discovery  that  it  also 
exists  in  small  quantities  on  the  earth.  A  fact  which 
may  have  a  significance  which  we  cannot  at  present 
see  is  that  the  emanation  from  radium  gradually  and 
spontaneously  changes  into  helium,  an  alchemist ical 
feat  of  nature  that  has  opened  many  curious  vistas 
to  speculative  thinkers.  The  eruptive  prominences, 
which  do  not  spread  horizontally  like  the  others,  but 
ascend  with  marvellous  velocity  to  elevations  of  half 
a  million  miles  or  more,  are  apparently  composed 
largely  of  metallic  vapors — i.e.,  metals  which  are 
usually  solid  on  the  earth,  but  which  at  solar  tem- 
peratures are  kept  in  a  volatilized  state.  The 
velocity  of  their  ascent  occasionally  amounts  to 
three  hundred  or  four  hundred  miles  per  second.  It 
is  known  from  mathematical  considerations  that  the 
gravitation  of  the  sun  would  not  be  able  to  bring  back 
any  body  that  started  from  its  surface  with  a  velocity 
exceeding  three  hundred  and  eighty-three  miles  per 
second ;  so  it  is  evident  that  some  of  the  matter  hurled 
forth  in  eruptive  prominences  may  escape  from 
solar  control  and  go  speeding  out  into  space,  cooling 

1 20 




and  condensing  into  solid  masses.  There  seems  to  be 
no  reason  why  some  of  the  projectiles  from  the  sun 
might  not  reach  the  planets.  Here,  then,  we  have, 
on  a  relatively  small  scale,  explosions  recalling  those 
which  it  has  been  imagined  may  be  the  originating 
cause  of  some  of  the  sudden  phenomena  of  the  stellar 

Of  the  sun-spots  it  is  not  our  intention  here  specially 
to  speak,  but  they  evidently  have  an  intimate  con- 
nection with  eruptive  prominences,  as  well  as  some 
relation,  not  yet  fully  understood,  with  the  corona. 
Of  the  real  cause  of  sun-spots  we  know  virtually  noth- 
ing, but  recent  studies  by  Professor  Hale  and  others 
have  revealed  a  strange  state  of  things  in  the  clouds  of 
metallic  vapors  floating  above  them  and  their  sur- 
roundings. Evidences  of  a  cyclonic  tendency  have 
been  found,  and  Professor  Hale  has  proved  that  sun- 
spots  are  strong  magnetic  fields,  and  consist  of 
columns  of  ionized  vapors  rotating  in  opposite 
directions  in  the  two  hemispheres.  A  fact  which  may 
have  the  greatest  significance  is  that  titanium  and 
vanadium  have  been  found  both  in  sun-spots  and 
in  the  remarkable  variable  Mira  Ceti,  a  star  which 
every  eleven  months,  or  thereabout,  flames  up  with 
great  brilliancy  and  then  sinks  back  to  invisibility 
with  the  naked  eye.  It  has  been  suggested  that  sun- 
spots  are  indications  of  the  beginning  of  a  process  in 
the  sun  which  will  be  intensified  until  it  falls  into  the 
state  of  such  a  star  as  Mira.  Stars  very  far  advanced 
in  evolution,  without  showing  variability,  also  ex- 
hibit similar  spectra ;  so  that  there  is  much  reason  for 
regarding  sunspots  as  emblems  of  advancing  age. 



The  association  of  the  corona  with  sun-spots  is  less 
evident  than  that  of  the  eruptive  prominences;  still 
such  an  association  exists,  for  the  form  and  extent  of 
the  corona  vary  with  the  sun-spot  period  of  which  we 
shall  presently  speak.  The  constitution  of  the  corona 
remains  to  be  discovered.  It  is  evidently  in  part 
gaseous,  but  it  also  probably  contains  matter  in  the 
form  of  dust  and  small  meteors.  It  includes  one 
substance  altogether  mysterious — ' '  coronium . ' '  There 
are  reasons  for  thinking  that  this  may  be  the  lightest 
of  all  the  elements,  and  Professor  Young,  its  dis- 
coverer, said  that  it  was  "absolutely  unique  in  nature; 
utterly  distinct  from  any  other  known  form  of  matter, 
terrestrial,  solar,  or  cosmical."  The  enormous  ex- 
tent of  the  corona  is  one  of  its  riddles.  Since  the 
development  of  the  curious  subject  of  the  "pressure  of 
light"  it  has  been  proposed  to  account  for  the  sus- 
tentation  of  the  corona  by  supposing  that  it  is  borne 
upon  the  billows  of  light  continually  poured  out  from 
the  sun.  Experiment  has  proved,  what  mathemat- 
ical considerations  had  previously  pointed  out  as 
probable,  that  the  waves  of  light  exert  a  pressure  or 
driving  force,  which  becomes  evident  in  its  effects  if 
the  body  acted  upon  is  sufficiently  small.  In  that 
case  the  light  pressure  will  prevail  over  the  attraction 
of  gravitation,  and  propel  the  attenuated  matter 
away  from  the  sun  in  the  teeth  of  its  attraction.  The 
earth  itself  would  be  driven  away  if,  instead  of  con- 
sisting of  a  solid  globe  of  immense  aggregate  mass, 
it  were  a  cloud  of  microscopic  particles.  The  reason 
is  that  the  pressure  varies  in  proportion  to  the  sur- 
face of  the  body  acted  upon,  while  the  gravitational 



attraction  is  proportional  to  the  volume,  or  the  total 
amount  of  matter  in  the  body.  But  the  surface  of 
any  body  depends  upon  the  square  of  its  diameter, 
while  the  volume  depends  upon  the  cube  of  the 
diameter.  If,  for  instance,  the  diameter  is  represented 
by  4,  the  surface  will  be  proportional  to  4  x  4,  or  16, 
and  the  volume  to  4  x  4  x  4,  or  64;  but  if  the  diameter 
is  taken  as  2,  the  surface  will  be  2  x  2,  or  4,  and  the 
volume  2  x  2  x  2,  or  8.  Now,  the  ratio  of  4  to  8  is 
twice  as  great  as  that  of  16  to  64.  If  the  diameter 
is  still  further  decreased,  the  ratio  of  the  surface  to  the 
volume  will  proportionally  grow  larger;  in  other  words, 
the  pressure  will  gain  upon  the  attraction,  and  what- 
ever their  original  ratio  may  have  been,  a  time  will 
come,  if  the  diminution  of  size  continues,  when  the 
pressure  will  become  more  effective  than  the  attraction, 
and  the  body  will  be  driven  away.  Supposing  the  par- 
ticles of  the  corona  to  be  below  the  critical  size  for  the 
attraction  of  a  mass  like  that  of  the  sun  to  control 
them,  they  would  be  driven  off  into  the  surrounding 
space  and  appear  around  the  sun  like  the  clouds  of  dust 
around  a  mill.  We  shall  return  to  this  subject  in 
connection  with  the  Zodiacal  Light,  the  Aurora,  and 

On  the  other  hand,  there  are  parts  of  the  corona 
which  suggest  by  their  forms  the  play  of  electric  or 
magnetic  forces.  This  is  beautifully  shown  in  some 
of  the  photographs  that  have  been  made  of  the  corona 
during  recent  eclipses.  Take,  for  instance,  that  of  the 
eclipse  of  1900.  The  sheaves  of  light  emanating  from 
the  poles  look  precisely  like  the  "lines  of  force"  sur- 
rounding the  poles  of  a  magnet,  It  will  be  noticed 


in  this  photograph  that  the  corona  appears  to  consist 
of  two  portions:  one  comprising  the  polar  rays  just 
spoken  of,  and  the  other  consisting  of  the  broader, 
longer,  and  less-defined  masses  of  light  extending  out 
from  the  equatorial  and  middle-latitude  zones.  Yet 
even  in  this  more  diffuse  part  of  the  phenomenon  one 
can  detect  the  presence  of  submerged  curves  bearing 
more  or  less  resemblance  to  those  about  the  poles. 
Just  what  part  electricity  or  electro-magnetism  plays 
in  the  mechanism  of  the  solar  radiation  it  is  im- 
possible to  say,  but  on  the  assumption  that  it  is  a  very 
important  part  is  based  the  hypothesis  that  there 
exists  a  direct  solar  influence  not  only  upon  the  mag- 
netism, but  upon  the  weather  of  the  earth.  This  hy- 
pothesis has  been  under  discussion  for  half  a  century, 
and  still  we  do  not  know  just  how  much  truth  it  rep- 
resents. It  is  certain  that  the  outbreak  of  great  dis- 
turbances on  the  sun,  accompanied  by  the  formation  of 
sun-spots  and  the  upshooting  of  eruptive  prominences 
(phenomena  which  we  should  naturally  expect  to  be 
attended  by  action),  have  been  instantly  followed  by 
corresponding  " magnetic  storms"  on  the  earth  and 
brilliant  displays  of  the  auroral  lights.  There  have 
been  occasions  when  the  influence  has  manifested 
itself  in  the  most  startling  ways,  a  great  solar  outburst 
being  followed  by  a  mysterious  gripping  of  the  cable 
and  telegraph  systems  of  the  world,  as  if  an  in  visible 
and  irresistible  hand  had  seized  them.  Messages  are 
abruptly  cut  off,  sparks  leap  from  the  telegraph  in- 
struments, and  the  entire  earth  seems  to  have  been 
thrown  into  a  magnetic  flurry.  These  occurrences 
affect  the  mind  with  a  deep  impression  of  the  depend- 



ence  of  our  planet  on  the  sun,  such  as  we  do  not  derive 
from  the  more  familiar  action  of  the  sunlight  on  the 
growth  of  plants  and  other  phenomena  of  life  de- 
pending on  solar  influences. 

Perhaps  the  theory  of  solar  magnetic  influence  upon 
the  weather  is  best  known  in  connection  with  the 
"sun-spot  cycle."  This,  at  any  rate,  is,  as  already 
remarked,  closely  associated  with  the  corona.  Its 
existence  was  discovered  in  1843  by  the  German  as- 
tronomer Schwabe.  It  is  a  period  of  variable  length, 
averaging  about  eleven  years,  during  which  the  num- 
ber of  spots  visible  on  the  sun  first  increases  to  a 
maximum,  then  diminishes  to  a  minimum,  and  finally 
increases  again  to  a  maximum.  For  unknown  reasons 
the  period  is  sometimes  two  or  three  years  longer  than 
the  average  and  sometimes  as  much  shorter.  Never- 
theless, the  phenomena  always  recur  in  the  same  order. 
Starting,  for  instance,  with  a  time  when  the  observer 
can  find  few  or  no  spots,  they  gradually  increase  in 
number  and  size  until  a  maximum,  in  both  senses,  is 
reached,  during  which  the  spots  are  often  of  enormous 
size  and  exceedingly  active.  After  two  or  three  years 
they  begin  to  diminish  in  number,  magnitude,  and 
activity  until  they  almost  or  quite  disappear.  A 
strange  fact  is  that  when  a  new  period  opens,  the  spots 
appear  first  in  high  northern  and  southern  latitudes, 
far  from  the  solar  equator,  and  as  the  period  ad- 
vances they  not  only  increase  in  number  and  size,  but 
break  out  nearer  and  nearer  to  the  equator,  the  last 
spots  of  a  vanishing  period  sometimes  lingering  in  the 
equatorial  region  after  the  advance-guard  of  its  suc- 
cessor has  made  its  appearance  in  the  high  latitudes. 



Spots  are  never  seen  on  the  equator  nor  near  the 
poles.  It  was  not  very  long  after  the  discovery  of 
the  sun-spot  cycle  that  the  curious  observation  was 
made  that  a  striking  coincidence  existed  between  the 
period  of  the  sun-spots  and  another  period  affecting 
the  general  magnetic  condition  of  the  earth.  When  a 
curved  line  representing  the  varying  number  of  sun- 
spots  was  compared  with  another  curve  showing  the 
variations  in  the  magnetic  state  of  the  earth  the  two 
were  seen  to  be  in  almost  exact  accord,  a  rise  in  one 
curve  corresponding  to  a  rise  in  the  other,  and  a  fall 
to  a  fall.  Continued  observation  has  proved  that  this 
is  a  real  coincidence  and  not  an  accidental  one,  so 
that  the  connection,  although  as  yet  unexplained,  is 
accepted  as  established.  But  does  the  influence  ex- 
tend further,  and  directly  affect  the  weather  and  the 
seasons  as  well  as  the  magnetic  elements  on  the  earth  ? 
A  final  answer  to  this  question  cannot  yet  be  given, 
for  the  evidence  is  contradictory,  and  the  interpreta- 
tions put  upon  it  depend  largely  on  the  predilections 
of  the  judges. 

But,  in  a  broad  sense,  the  sun-spots  and  the  phenom- 
ena connected  with  them  must  have  a  relation  to 
terrestrial  meteorology,  for  they  prove  the  sun  to  be  a 
variable  star.  Reference  was  made,  a  few  lines  above, 
to  the  resemblance  of  the  spectra  of  sun-spots  to 
those  of  certain  stars  which  seem  to  be  failing  through 
age.  This  in  itself  is  extremely  suggestive ;  but  if  this 
resemblance  had  never  been  discovered,  we  should 
have  been  justified  in  regarding  the  sun  as  variable 
in  its  output  of  energy;  and  not  only  variable,  but 
probably  increasingly  so.  The  very  inequalities  in 



the  sun-spot  cycle  are  suspicious.  When  the  sun  is 
most  spotted  its  total  light  may  be  reduced  by  one- 
thousandth  part,  although  it  is  by  no  means  certain 
that  its  outgiving  of  thermal  radiations  is  then  re- 
duced. A  loss  of  one-thousandth  of  its  luminosity 
would  correspond  to  a  decrease  of  .0025  of  a  stellar 
magnitude,  considering  the  sun  as  a  star  viewed  from 
distant  space.  So  slight  a  change  would  not  be  per- 
ceptible; but  it  is  not  alone  sun-spots  which  obscure 
the  solar  surface,  its  entire  globe  is  enveloped  with  an 
obscuring  veil.  When  studied  with  a  powerful  tele- 
scope the  sun's  surface  is  seen  to  be  thickly  mottled 
with  relatively  obscure  specks,  so  numerous  that  it 
has  been  estimated  that  they  cut  off  from  one-tenth 
to  one-twentieth  of  the  light  that  we  should  receive 
from  it  if  the  whole  surface  were  as  brilliant  as  its 
brightest  parts.  The  condition  of  other  stars  warrants 
the  conclusion  that  this  obscuring  envelope  is  the  prod- 
uct of  a  process  of  refrigeration  which  will  gradually 
make  the  sun  more  and  more  variable  until  its  history 
ends  in  extinction.  Looking  backward,  we  see  a  time 
when  the  sun  must  have  been  more  brilliant  than  it  is 
now.  At  that  time  it  probably  shone  with  the  blind- 
ing white  splendor  of  such  stars  as  Sirius,  Spica,  and 
Vega;  now  it  resembles  the  relatively  dull  Procyon; 
in  time  it  will  turn  ruddy  and  fall  into  the  closing 
cycle  represented  by  Antares.  Considering  that  once 
it  must  have  been  more  radiantly  powerful  than  at 
present,  one  is  tempted  to  wonder  if  that  could  have 
been  the  time  when  tropical  life  flourished  within  the 
earth's  polar  circles,  sustained  by  a  vivific  energy 
in  the  sun  which  it  has  now  lost. 



The  corona,  as  we  have  said,  varies  with  the  sun- 
spot  cycle.  When  the  spots  are  abundant  and  active  the 
corona  rises  strong  above  the  spotted  zones,  forming 
immense  beams  or  streamers,  which  on  one  occasion, 
at  least,  had  an  observed  length  of  ten  million  miles. 
At  the  time  of  a  spot  minimum  the  corona  is  less  brill- 
iant and  has  a  different  outline.  It  is  then  that  the 
curved  polar  rays  are  most  conspicuous.  Thus  the 
vast  banners  of  the  sun,  shaken  out  in  the  eclipse,  are 
signals  to  tell  of  its  varying  state,  but  it  will  probably 
be  long  before  we  can  read  correctly  their  messages. 



HPHERE  is  a  singular  phenomenon  in  the  sky — one 
1  of  the  most  puzzling  of  all  —  which  has  long 
arrested  the  attention  of  astronomers,  defying  their 
efforts  at  explanation,  but  which  probably  not  one 
in  a  hundred,  and  possibly  not  one  in  a  thousand,  of 
the  readers  of  this  book  has  ever  seen.  Yet  its 
name  is  often  spoken,  and  it  is  a  conspicuous  object 
if  one  knows  when  and  where  to  look  for  it,  and 
when  well  seen  it  exhibits  a  mystical  beauty  which 
at  the  same  time  charms  and  awes  the  beholder.  It 
is  called  "The  Zodiacal  Light,"  because  it  lies  within 
the  broad  circle  of  the  Zodiac,  marking  the  sun's 
apparent  annual  path  through  the  stars.  What  it  is 
nobody  has  yet  been  able  to  find  out  with  certainty, 
and  books  on  astronomy  usually  speak  of  it  with 
singular  reserve.  But  it  has  given  rise  to  many 
remarkable  theories,  and  a  true  explanation  of  it 
would  probably  throw  light  on  a  great  many  other 
celestial  mysteries.  The  Milky  Way  is  a  more  won- 
derful object  to  look  upon,  but  its  nature  can  be  com- 
prehended, while  there  is  a  sort  of  uncanniness  about 
the  Zodiacal  Light  which  immediately  impresses  one 
upon  seeing  it,  for  its  part  in  the  great  scheme  of 
extra-terrestrial  affairs  is  not  evident. 


If  you  are  out-of-doors  soon  after  sunset — say,  on  an 
evening  late  in  the  month  of  February — you  may  per- 
ceive, just  after  the  angry  flush  of  the  dying  winter's 
day  has  faded  from  the  sky,  a  pale  ghostly  presence 
rising  above  the  place  where  the  sun  went  down. 
The  writer  remembers  from  boyhood  the  first  time  it 
was  pointed  out  to  him  and  the  unearthly  impression 
that  it  made,  so  that  he  afterward  avoided  being  out 
alone  at  night,  fearful  of  seeing  the  spectral  thing 
again.  The  phenomenon  brightens  slowly  with  the 
fading  of  the  twilight,  and  soon  distinctly  assumes 
the  shape  of  an  elongated  pyramid  of  pearly  light, 
leaning  toward  the  south  if  the  place  of  observation 
is  in  the  northern  hemisphere.  It  does  not  impress  the 
observer  at  all  in  the  same  manner  as  the  Milky  Way; 
that  looks  far  off  and  is  clearly  among  the  stars,  but 
the  Zodiacal  Light  seems  closer  at  hand,  as  if  it  were 
something  more  intimately  concerning  the  earth.  To 
all  it  immediately  suggests  a  connection,  also,  with 
the  sunken  sun.  If  the  night  is  clear  and  the  moon 
absent  (and  if  you  are  in  the  country,  for  city  lights 
ruin  the  spectacles  of  the  sky),  you  will  be  able  to 
watch  the  apparition  for  a  long  time.  You  will 
observe  that  the  Light  is  brightest  near  the  horizon, 
gradually  fading  as  the  pyramidal  beam  mounts 
higher,  but  in  favorable  circumstances  it  may  be 
traced  nearly  to  the  meridian  south  of  the  zenith, 
where  its  apex  at  last  vanishes  in  the  starlight.  It 
continues  visible  during  the  evenings  of  March  and 
part  of  April,  after  which,  ordinarily,  it  is  seen  no 
more,  or  if  seen  is  relatively  faint  and  unimpressive. 
But  when  autumn  comes  it  appears  again,  this  time 



not  like  a  wraith  hovering  above  the  westward  tomb  of 
the  day-god,  but  rather  like  a  spirit  of  the  morning 
announcing  his  reincarnation  in  the  east. 

The  reason  why  the  Zodiacal  Light  is  best  seen  in 
our  latitudes  at  the  periods  just  mentioned  is  because 
at  those  times  the  Zodiac  is  more  nearly  perpendicular 
to  the  horizon,  first  in  the  west  and  then  in  the  east; 
and,  since  the  phenomenon  is  confined  within  the 
borders  of  the  Zodiac,  it  cannot  be  favorably  placed 
for  observation  when  the  zodiacal  plane  is  but  slightly 
inclined  to  the  horizon.  Its  faint  light  requires  the 
contrast  of  a  background  of  dark  sky  in  order  to  be 
readily  perceptible.  But  within  the  tropics,  where 
the  Zodiac  is  always  at  a  favorable  angle,  the  mys- 
terious light  is  more  constantly  visible.  Nearly  all 
observant  travellers  in  the  equatorial  regions  have 
taken  particular  note  of  this  phenomenon,  for  being 
so  much  more  conspicuous  there  than  in  the  temperate 
zones  it  at  once  catches  the  eye  and  holds  the  atten- 
tion as  a  novelty.  Humboldt  mentions  it  many  times 
in  his  works,  for  his  genius  was  always  attracted  by 
things  out  of  the  ordinary  and  difficult  of  explana- 
tion, and  he  made  many  careful  observations  on  its 
shape,  its  brilliancy,  and  its  variations;  for  there  can 
be  no  doubt  that  it  does  vary,  and  sometimes  to  an 
astonishing  degree.  It  is  said  that  it  once  remained 
practically  invisible  in  Europe  for  several  years  in 
succession.  During  a  trip  to  South  Africa  in  1909  an 
English  astronomer,  Mr.  E.  W.  Maunder,  found  a 
remarkable  difference  between  the  appearance  of  the 
Zodiacal  Light  on  his  going  and  coming  voyages. 
In  fact,  when  crossing  the  equator  going  south  he  did 


not  see  it  at  all;  but  on  returning  he  had,  on  March 
6th,  when  one  degree  south  of  the  equator,  a  memora- 
ble view  of  it.  "It  was  a  bright,  clear  night,  and  the 
Zodiacal  Light  was  extraordinarily  brilliant — brighter 
than  he  had  ever  seen  it  before.  The  Milky  Way 
was  not  to  be  compared  with  it.  The  brightest  part 
extended  to  75°  from  the  sun.  There  was  a  faint 
and  much  narrower  extension  which  they  could  just 
make  out  beyond  the  Pleiades  along  the  ecliptic,  but 
the  greater  part  of  the  Zodiacal  Light  showed  as  a 
broad  truncated  column,  and  it  did  not  appear  nearly 
as  conical  as  he  had  before  seen  it." 

When  out  of  the  brief  twilight  of  intertropical 
lands,  where  the  sun  drops  vertically  to  the  horizon 
and  night  rushes  on  like  a  wave  of  darkness,  the 
Zodiacal  Light  shoots  to  the  very  zenith,  its  color  is 
described  as  a  golden  tint,  entirely  different  from  the 
silvery  sheen  of  the  Milky  Way.  If  I  may  venture 
again  to  refer  to  personal  experiences  and  impressions, 
I  will  recall  a  view  of  the  Zodiacal  Light  from  the 
summit  of  the  cone  of  Mt.  Etna  in  the  autumn  of 
the  year  1896  (more  briefly  described  in  Astronomy 
with  the  Naked  Eye).  There  are  few  lofty  mountains 
so  favorably  placed  as  Etna  for  observations  of  this 
kind.  It  was  once  resorted  to  by  Prof.  George  E. 
Hale,  in  an  attempt  to  see  the  solar  corona  without  an 
eclipse.  Rising  directly  from  sea-level  to  an  elevation 
of  nearly  eleven  thousand  feet,  the  observer  on  its 
summit  at  night  finds  himself,  as  it  were,  lost  in  the 
midst  of  the  sky.  But  for  the  black  flanks  of  the 
great  cone  on  which  he  stands  he  might  fancy  himself 
to  be  in  a  balloon.  On  the  occasion  to  which  I  refer 


the  world  beneath  was  virtually  invisible  in  the 
moonless  night.  The  blaze  of  the  constellations  over- 
head was  astonishingly  brilliant,  yet  amid  all  their 
magnificence  my  attention  was  immediately  drawn 
to  a  great  tapering  light  that  sprang  from  the  place 
on  the  horizon  where  the  sun  would  rise  later,  and 
that  seemed  to  be  blown  out  over  the  stars  like  a  long, 
luminous  veil.  It  was  the  finest  view  of  the  Zodiacal 
Light  that  I  had  ever  enjoyed — thrilling  in  its  strange- 
ness— but  I  was  almost  disheartened  by  the  indif- 
ference of  my  guide,  to  whom  it  was  only  a  light  and 
nothing  more.  If  he  had  no  science,  he  had  less 
poetry — rather  a  remarkable  thing,  I  thought,  for  a 
child  of  his  clime.  The  Light  appeared  to  me  to  be 
distinctly  brighter  than  the  visible  part  of  the  Milky 
Way  which  included  the  brilliant  stretches  in  Auriga 
and  Perseus,  and  its  color,  if  one  may  speak  of  color 
in  connection  with  such  an  object,  seemed  richer  than 
that  of  the  galactic  band ;  but  I  did  not  think  of  it  as 
yellow,  although  Humboldt  has  described  it  as  re- 
sembling a  golden  curtain  drawn  over  the  stars,  and 
Du  Chaillu  in  Equatorial  Africa  found  it  of  a  bright 
yellow  color.  It  may  vary  in  color  as  in  con- 
spicuousness.  The  fascination  of  that  extraordinary 
sight  has  never  faded  from  my  memory.  I  turned  to 
regard  it  again  and  again,  although  I  had  never  seen 
the  stellar  heavens  so  brilliant,  and  it  was  one  of  the 
last  things  I  looked  for  when  the  morning  glow  began 
softly  to  mount  in  the  east,  and  Sicily  and  the  Medi- 
terranean slowly  emerged  from  the  profound  shadow 
beneath  us. 
The  Zodiacal  Light  seems  never  to  have  attracted 


from  astronomers  in  general  the  amount  of  careful 
attention  that  it  deserves;  perhaps  because  so  little 
can  really  be  made  of  it  as  far  as  explanation  is  con- 
cerned. I  have  referred  to  the  restraint  that  scientific 
writers  apparently  feel  in  speaking  of  it.  The  grounds 
for  speculation  that  it  affords  may  be  too  scanty  to 
lead  to  long  discussions,  yet  it  piques  curiosity,  and 
as  we  shall  see  in  a  moment  has  finally  led  to  a  most 
interesting  theory.  Once  it  was  the  subject  of  an 
elaborate  series  of  studies  which  carried  the  observer 
all  round  the  world.  That  was  in  1845-46,  during 
the  United  States  Exploring  Expedition  that  visited 
the  then  little  known  Japan.  The  chaplain  of  the 
fleet,  the  Rev.  Mr.  Jones,  went  out  prepared  to  study 
the  mysterious  light  in  all  its  phases.  He  saw  it  from 
many  latitudes  on  both  sides  of  the  equator,  and  the 
imagination  cannot  but  follow  him  with  keen  interest 
in  his  world-circling  tour,  keeping  his  eyes  every 
night  fixed  upon  the  phantasm  overhead,  whose 
position  shifted  with  that  of  the  hidden  sun.  He 
demonstrated  that  the  glow  extends  at  times  com- 
pletely across  the  celestial  dome,  although  it  is  rel- 
atively very  faint  directly  behind  the  earth.  On  his 
return  the  government  published  a  large  volume  of  his 
observations,  in  which  he  undertook  to  show  that  the 
phenomenon  was  due  to  the  reflection  of  sunlight  from 
a  ring  of  meteoric  bodies  encircling  the  earth.  But, 
after  all,  this  elaborate  investigation  settled  nothing. 
Prof.  E.  E.  Barnard  has  more  recently  devoted 
much  attention  to  the  Zodiacal  Light,  as  well  as  to  a 
strange  attendant  phenomenon  called  the  "Gegen- 
schein,"  or  Counterglow,  because  it  always  appears  at 



that  point  in  the  sky  which  is  exactly  opposite  to  the 
sun.  The  Gegenschein  is  an  extremely  elusive 
phenomenon,  suitable  only  for  eyes  that  have  been 
specially  trained  to  see  it.  Professor  Newcomb  has 
cautiously  remarked  that  "it  is  said  that  in  that  point 
of  the  heavens  directly  opposite  to  the  sun  there  is 
an  elliptical  patch  of  light.  .  .  .  This  phenomenon  is  so 
difficult  to  account  for  that  its  existence  is  sometimes 
doubted;  yet  the  testimony  in  its  favor  is  difficult  to 
set  aside."  It  certainly  cannot  be  set  aside  at  all 
since  the  observations  of  Barnard.  I  recall  an  at- 
tempt to  see  it  under  his  guidance  during  a  visit  to 
Mount  Hamilton,  when  he  was  occupied  there  with  the 
Lick  telescope.  Of  course,  both  the  Gegenschein  and 
the  Zodiacal  Light  are  too  diffuse  to  be  studied  with 
telescopes,  which,  so  to  speak,  magnify  them  out  of 
existence.  They  can  only  be  successfully  studied 
with  the  naked  eye,  since  every  faintest  glimmer  that 
they  afford  must  be  utilized.  This  is  especially  true 
of  the  Gegenschein.  At  Mount  Hamilton,  Mr.  Barnard 
pointed  out  to  me  its  location  with  reference  to  cer- 
tain stars,  but  with  all  my  gazing  I  could  not  be  sure 
that  I  saw  it.  To  him,  on  the  contrary,  it  was  obvious; 
he  had  studied  it  for  months,  and  was  able  to  indicate 
its  shape,  its  boundaries,  its  diameter,  and  the  dec- 
lination of  its  centre  with  regard  to  the  ecliptic. 
There  is  not,  of  course,  the  shadow  of  a  doubt  of  the 
existence  of  the  Gegenschein,  and  yet  I  question  if  one 
person  in  a  million  has  ever  seen  or  ever  will  see  it. 
The  Zodiacal  Light,on  the  other  hand,  is  plain  enough, 
provided  that  the  time  and  the  circumstances  of  the 
observation  are  properly  chosen. 


In  the  attempts  to  explain  the  Zodiacal  Light,  the 
favorite  hypothesis  has  been  that  it  is  an  appendage 
of  the  sun — perhaps  simply  an  extension  of  the  corona 
in  the  plane  of  the  ecliptic,  which  is  not  very  far  from 
coinciding  with  that  of  the  sun's  equator.  This  idea 
is  quite  a  natural  one,  because  of  the  evident  relation 
of  the  light  to  the  position  of  the  sun.  The  vast  ex- 
tension of  the  equatorial  wings  of  the  corona  in  1878 
gave  apparent  support  to  this  hypothesis ;  if  the  sub- 
stance of  the  corona  could  extend  ten  million  miles 
from  the  sun,  why  might  it  not  extend  even  one 
hundred  million,  gradually  fading  out  beyond  the 
orbit  of  the  earth?  A  variation  of  this  hypothesis 
assumes  that  the  reflection  is  due  to  swarms  of  meteors 
circling  about  the  sun,  in  the  plane  of  its  equator,  all 
the  way  from  its  immediate  neighborhood  to  a  distance 
exceeding  that  of  the  earth.  But  in  neither  form  is 
the  hypothesis  satisfactory;  there  is  nothing  in  the 
appearance  of  the  corona  to  indicate  that  it  extends 
even  as  far  as  the  planet  Mercury,  while  as  to  meteors, 
the  orbits  of  the  known  swarms  do  not  accord  with 
the  hypothesis,  and  we  have  no  reason  to  believe  that 
clouds  of  others  exist  travelling  in  the  part  of  space 
where  they  would  have  to  be  in  order  to  answer  the 
requirements  of  the  theory.  The  extension  of  the 
corona  in  1878  did  not  resemble  in  its  texture  the 
Zodiacal  Light. 

Now,  it  has  so  often  happened  in  the  history  of 
science  that  an  important  discovery  in  one  branch 
has  thrown  unexpected  but  most  welcome  light  upon 
some  pending  problem  in  some  other  branch,  that  a 
strong  argument  might  be  based  upon  that  fact  alone 



against  the  too  exclusive  devotion  of  many  investi- 
gators to  the  narrow  lines  of  their  own  particular 
specialty;  and  the  Zodiacal  Light  affords  a  case  in 
point,  when  it  is  considered  in  connection  with  recent 
discoveries  in  chemistry  and  physics.  From  the  fact 
that  atoms  are  compound  bodies  made  up  of  corpuscles 
at  least  a  thousand  times  smaller  than  the  smallest 
known  atom — a  fact  which  astounded  most  men  of 
science  when  it  was  announced  a  few  years  ago — 
a  new  hypothesis  has  been  developed  concerning  the 
nature  of  the  Zodiacal  Light  (as  well  as  other  as- 
tronomical riddles),  and  this  hypothesis  comes  not 
from  an  astronomer,  but  from  a  chemist  and  physicist, 
the  Swede,  Svante  Arrhenius.  In  considering  an 
outline  of  this  new  hypothesis  we  need  neither  accept 
nor  reject  it;  it  is  a  case  rather  for  suspension  of 

To  begin  with,  it  carries  us  back  to  the  "pressure 
of  light"  mentioned  in  the  preceding  chapter.  The 
manner  in  which  this  pressure  is  believed  generally 
to  act  was  there  sufficiently  explained,  and  it  only 
remains  to  see  how  it  is  theoretically  extended  to  the 
particles  of  matter  supposed  to  constitute  the  Zodiacal 
Light.  We  know  that  corpuscles,  or  "fragments  of 
atoms"  negatively  electrified,  are  discharged  from 
hot  bodies.  Streams  of  these  "ions"  pour  from 
many  flames  and  from  molten  metals;  and  the  im- 
pact of  the  cathode  and  ultra-violet  rays  causes  them 
to  gush  even  from  cold  bodies.  In  the  vast  labora- 
tory of  the  sun  it  is  but  reasonable  to  suppose  that 
similar  processes  are  taking  place.  "As  a  very  hot 
metal  emits  these  corpuscles,"  says  Prof.  J.  J.  Thom- 


son,  "it  does  not  seem  an  improbable  hypothesis  that 
they  are  emitted  by  that  very  hot  body,  the  sun." 
Let  it  be  assumed,  then,  that  the  sun  does  emit  them ; 
what  happens  next?  Negatively  charged  corpuscles, 
it  is  known,  serve  as  nuclei  to  which  particles  of  matter 
in  the  ordinary  state  are  attracted,  and  it  is  probable 
that  those  emitted  from  the  sun  immediately  pick  up 
loads  in  this  manner  and  so  grow  in  bulk.  If  they 
grow  large  enough  the  gravitation  of  the  sun  draws 
them  back,  and  they  produce  a  negative  charge  in  the 
solar  atmosphere.  But  it  is  probable  that  many 
of  the  particles  do  not  attain  the  critical  size  which, 
according  to  the  principles  before  explained,  would 
enable  the  gravitation  of  the  sun  to  retain  them  in 
opposition  to  the  pressure  of  the  waves  of  light,  and 
with  these  particles  the  light  pressure  is  dominant. 
Clouds  of  them  may  be  supposed  to  be  continually 
swept  away  from  the  sun  into  surrounding  space, 
moving  mostly  in  or  near  the  plane  of  the  solar  equa- 
tor, where  the  greatest  activity,  as  indicated  by  sun- 
spots  and  related  phenomena,  is  taking  place.  As 
they  pass  outward  into  space  many  of  them  en- 
counter the  earth.  If  the  earth,  like  the  moon,  had 
no  atmosphere  the  particles  would  impinge  directly  on 
its  surface,  giving  it  a  negative  electric  charge.  But 
the  presence  of  the  atmosphere  changes  all  that,  for 
the  first  of  the  flying  particles  that  encounter  it  im- 
part to  it  their  negative  electricity,  and  then,  since 
like  electric  charges  repel  like,  the  storm  of  particles 
following  will  be  sheered  off  from  the  earth,  and  will 
stream  around  it  in  a  maze  of  hyperbolic  paths. 
Those  that  continue  on  into  space  beyond  the  earth 



may  be  expected  to  continue  picking  up  wandering 
particles  of  matter  until  their  bulk  has  become  so 
great  that  the  solar  attraction  prevails  again  over  the 
light  pressure  acting  upon  them,  and  they  turn  again 
sunward.  Passing  the  earth  on  their  return  they 
will  increase  the  amount  of  dust-clouds  careering  round 
it;  and  these  will  be  further  increased  by  the  action 
of  the  ultra-violet  rays  of  the  sunlight  causing  par- 
ticles to  shoot  radially  away  from  the  earth  when  the 
negative  charge  of  the  upper  atmosphere  has  reached 
a  certain  amount,  which  particles,  although  starting 
sunward,  will  be  swept  back  to  the  earth  with  the  on- 
coming streams.  As  the  final  result  of  all  this  ac- 
cumulation of  flying  and  gyrating  particles  in  the 
earth's  neighborhood,  we  are  told  that  the  latter  must 
be  transformed  into  the  semblance  of  a  gigantic  solid- 
headed  comet  provided  with  streaming  tails,  the 
longest  of  them  stretching  away  from  the  direction 
of  the  sun,  while  another  shorter  one  extends  toward 
the  sun.  This  shorter  tail  is  due  to  the  particles  that 
we  have  just  spoken  of  as  being  driven  sunward  from 
the  earth  by  the  action  of  ultra-violet  light.  No 
doubt  this  whole  subject  is  too  technical  for  popular 
statement;  but  at  any  rate  the  general  reader  can 
understand  the  picturesque  side  of  the  theory,  for 
its  advocates  assure  us  that  if  we  were  on  the  moon 
we  should  doubtless  be  able  to  see  the  comet-like  tails 
of  the  earth,  and  then  we  could  appreciate  the  part 
that  they  play  in  producing  the  phenomenon  of  the 
Zodiacal  Light. 

That  the  Light  as  we  see  it  could  be  produced  by 
the  reflection  of  sunlight  from  swarms  of  particles 



careering  round  the  earth  in  the  manner  supposed  by 
Arrhenius'  hypothesis  is  evident  enough;  and  it  will 
be  observed  that  the  new  theory,  after  all,  is  only  an- 
other variant  of  the  older  one  which  attributes  the 
Zodiacal  Light  to  an  extension  of  the  solar  corona. 
But  it  differs  from  the  older  theory  in  affording  an 
explanation  of  the  manner  in  which  the  extension  is 
effected,  and  it  differentiates  between  the  corona 
proper  and  the  streams  of  negative  particles  shot 
away  from  the  sun.  In  its  details  the  hypothesis  of 
Arrhenius  alsp  affords  an  explanation  of  many 
peculiarities  of  the  Zodiacal  Light,  such  as  that  it  is 
confined  to  the  neighborhood  of  the  ecliptic,  and  that 
it  is  stronger  on  the  side  of  the  earth  which  is  just 
turning  away  from  a  position  under  the  sun  than  on 
the  other  side;  but  it  would  carry  us  beyond  our 
limits  to  go  into  these  particulars.  The  Gegenschein, 
according  to  this  theory,  is  a  part  of  the  same  phenom- 
enon as  the  Zodiacal  Light,  for  by  the  laws  of 
perspective  it  is  evident  that  the  reflection  from  the 
streams  of  particles  situated  at  a  point  directly  op- 
posite to  the  sun  would  be  at  a  maximum,  and  this 
is  the  place  which  the  Gegenschein  occupies.  Apart 
from  its  geometrical  relations  to  the  position  of  the 
sun,  the  variability  of  the  Zodiacal  Light  appears  to 
affirm  its  solar  dependence,  and  this  too  would  be 
accounted  for  by  Arrhenius*  hypothesis  better  than 
by  the  old  theory  of  coronal  extension.  The  amount 
of  corpuscular  discharge  from  the  sun  must  nat- 
urally be  governed  by  the  state  of  relative  activity 
or  inactivity  of  the  latter,  and  this  could  not  but  be 
reflected  in  the  varying  splendor  of  the  Zodiacal 



Light.  But  much  more  extended  study  than  has 
yet  been  given  to  the  subject  will  be  required  before 
we  can  feel  that  we  know  with  reasonable  certainty 
what  this  mysterious  phenomenon  really  is.  By  the 
hypothesis  of  Arrhenius  every  planet  that  has  an 
atmosphere  must  have  a  Zodiacal  Light  attending  it, 
but  the  phenomenon  is  too  faint  for  us  to  be  able  to 
see  it  in  the  case,  for  instance,  of  Venus,  whose  at- 
mosphere is  very  abundant.  The  moon  has  no 
corresponding  "comet's  tail"  because,  as  already  ex- 
plained, of  the  lack  of  a  lunar  atmosphere  to  repel  the 
streams  by  becoming  itself  electrified;  but  if  there 
were  a  lunar  Zodiacal  Light,  no  doubt  we  could  see  it 
because  of  the  relative  nearness  of  our  satellite. 



ONE  of  the  most  vivid  recollections  of  my  early 
boyhood  is  that  of  seeing  my  father  return 
hastily  into  the  house  one  evening  and  call  out  to  the 
family:  "Come  outside  and  look  at  the  sky!"  Ours 
was  a  country  house  situated  on  a  commanding  site, 
and  as  we  all  emerged  from  the  doorway  we  were 
dumfounded  to  see  the  heavens  filled  with  pale  flames 
which  ran  licking  and  quivering  over  the  stars.  In- 
stantly there  sprang  into  my  terrified  mind  the 
recollection  of  an  awful  description  of  "the  Day  of 
Judgment'*  (the  Dies  Ircz),  which  I  had  heard  with 
much  perturbation  of  spirit  in  the  Dutch  Reformed 
church  from  the  lips  of  a  tall,  dark-browed,  dread  fully- 
in-earnest  preacher  of  the  old-fashioned  type.  My 
heart  literally  sank  at  sight  of  the  spectacle,  for  it 
recalled  the  preacher's  very  words;  it  was  just  as  he 
had  said  it  would  be,  and  it  needed  the  assured 
bearing  of  my  elders  finally  to  convince  me  that 

"That  Day  of  Wrath,  O  dreadful  day, 
When  Heaven  and  Earth  shall  pass  away, 
As  David  and  the  Sibyl  say," 

had  not  actually  come  upon  us.    And  even  the  older 
members  of  the  household  were  not  untouched  with 


•  '••'''Sir 



misgivings  when  menacing  spots  of  crimson  appeared, 
breaking  out  now  here,  now  there,  in  the  shuddering 
sky.  Toward  the  north  the  spectacle  was  appalling. 
A  huge  arch  spanned  an  unnaturally  dark  segment 
resting  on  the  horizon,  and  above  this  arch  sprang  up 
beams  and  streamers  in  a  state  of  incessant  agitation, 
sometimes  shooting  up  to  the  zenith  with  a  velocity 
that  took  one's  breath,  and  sometimes  suddenly  fall- 
ing into  long  ranks,  and  marching,  marching,  marching, 
like  an  endless  phalanx  of  fiery  spectres,  and  moving, 
as  I  remember,  always  from  east  to  west.  The  ab- 
solute silence  with  which  these  mysterious  evolutions 
were  performed  and  the  quavering  reflections  which 
were  thrown  upon  the  ground  increased  the  awfulness 
of  the  exhibition.  Occasionally  enormous  curtains 
of  lambent  flame  rolled  and  unrolled  with  a  majestic 
motion,  or  were  shaken  to  and  fro  as  if  by  a  mighty, 
noiseless  wind.  At  times,  too,  a  sudden  billowing 
rush  would  be  made  toward  the  zenith,  and  for  a 
minute  the  sky  overhead  would  glow  so  brightly  that 
the  stars  seemed  to  have  been  consumed.  The  spec- 
tacle continued  with  varying  intensity  for  hours. 

This  exhibition  occurred  in  Central  New  York, 
a  latitude  in  which  the  Aurora  Borealis  is  seldom  seen 
with  so  much  splendor.  I  remember  another  similar 
one  seen  from  the  city  of  New  York  in  November, 
1882.  On  this  last  occasion  some  observers  saw  a 
great  upright  beam  of  light  which  majestically  moved 
across  the  heavens,  stalking  like  an  apparition  in  the 
midst  of  the  auroral  pageant,  of  whose  general  move- 
ments it  seemed  to  be  independent,  maintaining  always 
its  upright  posture,  and  following  a  magnetic  parallel 



from  east  to  west.  This  mysterious  beam  was  seen 
by  no  less  than  twenty-six  observers  in  different  parts 
of  the  country,  and  a  comparison  of  their  observations 
led  to  a  curious  calculation  indicating  that  the 
apparition  was  about  one  hundred  and  thirty -three 
miles  tall  and  moved  at  the  speed  of  ten  miles  per 

But,  as  everybody  knows,  it  is  in  the  Arctic  regions 
that  the  Aurora,  or  the  "Northern  Lights/'  can  best 
be  seen.  There,  in  the  long  polar  night,  when  for 
months  together  the  sun  does  not  rise,  the  strange 
coruscations  in  the  sky  often  afford  a  kind  of  spectral 
daylight  in  unison  with  the  weird  scenery  of  the 
world  of  ice.  The  pages  in  the  narratives  of  Arctic 
exploration  that  are  devoted  to  descriptions  of  the 
wonderful  effects  of  the  Northern  Lights  are  second 
to  none  that  man  has  ever  penned  in  their  fascination. 
The  lights,  as  I  have  already  intimated,  display  as- 
tonishing colors,  particularly  shades  of  red  and  green, 
as  they  flit  from  place  to  place  in  the  sky.  The  dis- 
covery that  the  magnetic  needle  is  affected  by  the 
Aurora,  quivering  and  darting  about  in  a  state  of 
extraordinary  excitement  when  the  lights  are  play- 
ing in  the  sky,  only  added  to  the  mystery  of  the 
phenomenon  until  its  electro-magnetic  nature  had 
been  established.  This  became  evident  as  soon  as 
it  was  known  that  the  focus  of  the  displays  was  the 
magnetic  pole;  and  when  the  far  South  was  visited 
the  Aurora  Australis  was  found,  having  its  centre  at 
the  South  Magnetic  Pole.  Then,  if  not  before,  it  was 
clear  that  the  earth  was  a  great  globular  magnet, 
having  its  poles  of  opposite  magnetism,  and  that 



the  auroral  lights,  whatever  their  precise  cause  might 
be,  were  manifestations  of  the  magnetic  activity  of  our 
planet.  After  the  invention  of  magnetic  telegraphy 
it  was  found  that  whenever  a  great  Aurora  occurred 
the  telegraph  lines  were  interrupted  in  their  opera- 
tion, and  the  ocean  cables  ceased  to  work.  Such  a 
phenomenon  is  called  a  "magnetic  storm." 

The  interest  excited  by  the  Aurora  in  scientific 
circles  was  greatly  stimulated  when,  in  the  last  half 
of  the  nineteenth  century,  it  was  discovered  that  it  is 
a  phenomenon  intimately  associated  with  disturb- 
ances on  the  sun.  The  ancient  "Zurich  Chronicles," 
extending  from  the  year  1000  to  the  year  1800,  in 
which  both  sun-spots  visible  to  the  naked  eye  and 
great  displays  of  the  auroral  lights  were  recorded, 
first  set  Rudolph  Wolf  on  the  track  of  this  discovery. 
The  first  notable  proof  of  the  suspected  connection 
was  furnished  with  dramatic  emphasis  by  an  oc- 
currence which  happened  on  September  i,  1859. 
Near  noon  on  that  day  two  intensely  brilliant  points 
suddenly  broke  out  in  a  group  of  sun-spots  which  were 
under  observation  by  Mr.  R.  C.  Carrington  at  his 
observatory  at  Redhill,  England.  The  points  re- 
mained visible  for  not  more  than  five  minutes,  during 
which  interval  they  moved  thirty-five  thousand  miles 
across  the  solar  disk.  Mr.  R.  Hodgson  happened  to 
see  the  same  phenomenon  at  his  observatory  at 
Highgate,  and  thus  all  possibility  of  deception  was 
removed.  But  neither  of  the  startled  observers  could 
have  anticipated  what  was  to  follow,  and,  indeed,  it 
was  an  occurrence  which  has  never  been  precisely 
duplicated.  I  quote  the  eloquent  account  given  by 


Miss  Clerke,  in  her  History  of  Astronomy  During  the 
Nineteenth  Century. 

"This  unique  phenomenon  seemed  as  if  specially 
designed  to  accentuate  the  inference  of  a  sympathetic 
relation  between  the  earth  and  the  sun.  From  August 
28  to  September  4,  1859,  a  magnetic  storm  of  un- 
paralleled intensity,  extent,  and  duration  was  in 
progress  over  the  entire  globe.  Telegraphic  com- 
munication was  everywhere  interrupted — except,  in- 
deed, that  it  was  in  some  cases  found  practicable  to 
work  the  lines  without  batteries  by  the  agency  of  the 
earth-currents  alone;  sparks  issued  from  the  wires; 
gorgeous  auroras  draped  the  skies  in  solemn  crimson 
over  both  hemispheres,  and  even  in  the  tropics;  the 
magnetic  needle  lost  all  trace  of  continuity  in  its 
movements  and  darted  to  and  fro  as  if  stricken  with 
inexplicable  panic.  The  coincidence  was  even  closer. 
At  the  very  instant  of  the  solar  outburst  witnessed  by 
Carrington  and  Hodgson  the  photographic  apparatus 
at  Kew  registered  a  marked  disturbance  of  all  the 
three  magnetic  elements;  while  shortly  after  the  en- 
suing midnight  the  electric  agitation  culminated, 
thrilling  the  whole  earth  with  subtle  vibrations,  and 
lighting  up  the  atmosphere  from  pole  to  pole  with 
coruscating  splendors  which  perhaps  dimly  recall  the 
times  when  our  ancient  planet  itself  shone  as  a  star." 

If  this  amazing  occurrence  stood  alone,  and  as  I 
have  already  said  it  has  never  been  exactly  duplicated, 
doubt  might  be  felt  concerning  some  of  the  inferences 
drawn  from  it;  but  in  varying  forms  it  has  been  re- 
peated many  times,  so  that  now  hardly  any  one  ques- 
tions the  reality  of  the  assumed  connection  between 


solar  outbursts  and  magnetic  storms  accompanied  by 
auroral  displays  on  the  earth.  It  is  true  that  the  late 
Lord  Kelvin  raised  difficulties  in  the  way  of  the  hy- 
pothesis of  a  direct  magnetic  action  of  the  sun  upon 
the  earth,  because  it  seemed  to  him  that  an  inadmissi- 
ble quantity  of  energy  was  demanded  to  account  for 
such  action.  But  no  calculation  like  that  which  he 
made  is  final,  since  all  calculations  depend  upon  the 
validity  of  the  data ;  and  no  authority  is  unshakable  in 
science,  because  no  man  can  possess  omniscience.  It 
was  Lord  Kelvin  who,  but  a  few  years  before  the 
thing  was  actually  accomplished,  declared  that  aerial 
navigation  was  an  impracticable  dream,  and  demon- 
strated its  impracticability  by  calculation.  However 
the  connection  may  be  brought  about,  it  is  as  certain 
as  evidence  can  make  it  that  solar  outbursts  are  coin- 
cident with  terrestrial  magnetic  disturbances,  and 
coincident  in  such  a  way  as  to  make  the  inference  of  a 
causal  connection  irresistible.  The  sun  is  only  a  little 
more  than  a  hundred  times  its  own  diameter  away 
from  the  earth.  Why,  then,  with  the  subtle  connection 
between  them  afforded  by  the  ether  which  conveys 
to  us  the  blinding  solar  light  and  the  life-sustaining 
solar  heat,  should  it  be  so  difficult  to  believe  that  the 
sun's  enormous  electric  energies  find  a  way  to  us  also  ? 
No  doubt  the  impulse  coming  from  the  sun  acts  upon 
the  earth  after  the  manner  of  a  touch  upon  a  trigger, 
releasing  energies  which  are  already  stored  up  in  our 

But  besides  the  evidence  afforded  by  such  occur- 
rences as  have  been  related  of  an  intimate  connection 
between  solar  outbreaks  and  terrestrial  magnetic 


flurries,  attended  by  magnificent  auroral  displays, 
there  is  another  line  of  proof  pointing  in  the  same 
direction.  Thus,  it  is  known  that  the  sun-spot  period, 
as  remarked  in  a  preceding  chapter,  coincides  in  a 
most  remarkable  manner  with  the  periodic  fluctua- 
tions in  the  magnetic  state  of  the  earth.  This  coin- 
cidence runs  into  the  most  astonishing  details.  For 
instance,  when  the  sun-spot  period  shortens,  the 
auroral  period  shortens  to  precisely  the  same  extent; 
as  the  short  sun-spot  periods  usually  bring  the  most  in- 
tense outbreaks  of  solar  activity,  so  the  corresponding 
short  auroral  periods  are  attended  by  the  most  violent 
magnetic  storms;  a  secular  period  of  about  two 
hundred  and  twenty-two  years  affecting  sun-spots  is 
said  to  have  its  auroral  duplicate;  a  shorter  period  of 
fifty-five  and  a  half  years,  which  some  observers  be- 
lieve that  they  have  discovered  appears  also  to  be  com- 
mon to  the  two  phenomena;  and  yet  another  "super- 
posed" period  of  about  thirty-five  years,  which  some 
investigators  aver  exists,  affects  sun-spots  and  auroras 
alike.  In  short,  the  coincidences  are  so  numerous 
and  significant  that  one  would  have  to  throw  the 
doctrine  of  probability  to  the  winds  in  order  to  be 
able  to  reject  the  conclusion  to  which  they  so  plainly 

But  still  the  question  recurs:  How  is  the  influence 
transmitted  ?  Here  Arrhenius  comes  once  more  with 
his  hypothesis  of  negative  corpuscles,  or  ions,  driven 
away  from  the  sun  by  light-pressure — a  hypothesis 
which  seems  to  explain  so  many  things — and  offers 
it  also  as  an  explanation  of  the  way  in  which  the  sun 
creates  the  Aurora.  He  would  give  the  Aurora  the 


same  lineage  with  the  Zodiacal  Light.  To  under- 
stand the  application  of  this  theory  we  must  first 
recall  the  fact  that  the  earth  is  a  great  magnet  having 
its  two  opposite  poles  of  magnetism,  one  near  the 
Arctic  and  the  other  near  the  Antarctic  Circle.  Like 
all  magnets,  the  earth  is  surrounded  with  "lines  of 
force,"  which,  after  the  manner  of  the  curved  rays  we 
saw  in  the  photograph  of  a  solar  eclipse,  start  from 
a  pole,  rising  at  first  nearly  vertically,  then  bend 
gradually  over,  passing  high  above  the  equator,  and 
finally  descending  in  converging  sheaves  to  the 
opposite  pole.  Now  the  axis  of  the  earth  is  so 
placed  in  space  that  it  lies  at  nearly  a  right  angle  to 
the  direction  of  the  sun,  and  as  the  streams  of  nega- 
tively charged  particles  come  pouring  on  from  the 
sun  (see  the  last  preceding  chapter),  they  arrive  in 
the  greatest  numbers  over  the  earth's  equatorial 
regions.  There  they  encounter  the  lines  of  magnetic 
force  at  the  place  where  the  latter  have  their  greatest 
elevation  above  the  earth,  and  where  their  direction 
is  horizontal  to  the  earth's  surface.  Obeying  a  law 
which  has  been  demonstrated  in  the  laboratory,  the 
particles  then  follow  the  lines  of  force  toward  the 
poles.  While  they  are  above  the  equatorial  regions 
they  do  not  become  luminescent,  because  at  the  great 
elevation  that  they  there  occupy  there  is  virtually 
no  atmosphere ;  but  as  they  pass  on  toward  the  north 
and  the  south  they  begin  to  descend  with  the  lines  of 
force,  curving  down  to  meet  at  the  poles;  and,  en- 
countering a  part  of  the  atmosphere  comparable  in 
density  with  what  remains  in  an  exhausted  Crookes 
tube,  they  produce  a  glow  of  cathode  rays.  This  glow 


is  conceived  to  represent  the  Aurora,  which  may 
consequently  be  likened  to  a  gigantic  exhibition  of 
vacuum-tube  lights.  Anybody  who  recalls  his  student 
days  in  the  college  laboratory  and  who  has  witnessed 
a  display  of  Northern  Lights  will  at  once  recognize 
the  resemblance  between  them  in  colors,  forms,  and 
behavior.  This  resemblance  had  often  been  noted 
before  Arrhenius  elaborated  his  hypothesis. 

Without  intending  to  treat  his  interesting  theory 
as  more  than  a  possibly  correct  explanation  of  the 
phenomena  of  the  Aurora,  we  may  call  attention  to 
some  apparently  confirmatory  facts.  One  of  the 
most  striking  of  these  relates  to  a  seasonal  variation 
in  the  average  number  of  aurorse.  It  has  been  ob- 
served that  there  are  more  in  March  and  September 
than  at  any  other  time  of  the  year,  and  fewer  in  June 
and  December;  moreover  (and  this  is  a  delicate  test 
as  applied  to  the  theory),  they  are  slightly  rarer  in 
June  than  in  December.  Now  all  these  facts  seem 
to  find  a  ready  explanation  in  the  hypothesis  of  Ar- 
rhenius, thus:  (i)  The  particles  issuing  from  the  sun 
are  supposed  to  come  principally  from  the  regions 
whose  excitement  is  indicated  by  the  presence  of 
sun-spots  (which  accords  with  Hale's  observation  that 
sun-spots  are  columns  of  ionized  vapors),  and  these 
regions  have  a  definite  location  on  either  side  of  the 
solar  equator,  seldom  approaching  it  nearer  than 
within  5°  or  10°  north  or  south,  and  never  extending 
much  beyond  35°  toward  either  pole;  (2)  The  equator 
of  the  sun  is  inclined  about  7°  to  the  plane  of  the 
earth's  orbit,  from  which  it  results  that  twice  in  a 
year — viz.,  in  June  and  December — the  earth  is  directly 



over  the  solar  equator,  and  twice  a  year — viz.,  in 
March  and  September — when  it  is  farthest  north  or 
south  of  the  solar  equator,  it  is  over  the  inner  edge 
of  the  sun-spot  belts.  Since  the  corpuscles  must  be 
supposed  to  be  propelled  radially  from  the  sun,  few 
will  reach  the  earth  when  the  latter  is  over  the  solar 
equator  in  June  and  December,  but  when  it  is  over, 
or  nearly  over,  the  spot  belts,  in  March  and  September, 
it  will  be  in  the  line  of  fire  of  the  more  active  parts 
of  the  solar  surface,  and  relatively  rich  streams  of 
particles  will  reach  it.  This,  as  will  be  seen  from 
what  has  been  said  above,  is  in  strict  accord  with  the 
observed  variations  in  the  frequency  of  auroras. 
Even  the  fact  that  somewhat  fewer  auroras  are  seen 
in  June  than  in  December  also  finds  its  explanation 
in  the  known  fact  that  the  earth  is  about  three  million 
miles  nearer  the  sun  in  the  winter  than  in  the  summer, 
and  the  number  of  particles  reaching  it  will  vary, 
like  the  intensity  of  light,  inversely  as  the  square  of 
the  distance.  These  coincidences  are  certainly  very 
striking,  and  they  have  a  cumulative  force.  If  we 
accept  the  theory,  it  would  appear  that  we  ought  to 
congratulate  ourselves  that  the  inclination  of  the 
sun's  equator  is  so  slight,  for  as  things  stand  the 
earth  is  never  directly  over  the  most  active  regions 
of  the  sun-spots,  and  consequently  never  suffers  from 
the  maximum  bombardment  of  charged  particles  of 
which  the  sun  is  capable.  Incessant  auroral  dis- 
plays, with  their  undulating  draperies,  flitting  colors, 
and  marching  columns  might  not  be  objectionable 
from  the  point  of  view  of  picturesqueness,  but  one 
magnetic  storm  of  extreme  intensity  following  closely 
9  159 


upon  the  heels  of  another,  for  months  on  end,  crazing 
the  magnetic  needle  and  continually  putting  the 
telegraph  and  cable  lines  out  of  commission,  to  say 
nothing  of  their  effect  upon  " wireless  telegraphy," 
would  hardly  add  to  the  charms  of  terrestrial  exist- 

One  or  two  other  curious  points  in  connection  with 
Arrhenius'  hypothesis  may  be  mentioned.  First, 
the  number  of  auroras,  according  to  his  explanation, 
ought  to  be  greatest  in  the  daytime,  when  the  face 
of  the  earth  on  the  sunward  side  is  directly  exposed 
to  the  atomic  bombardment.  Of  course  visual  ob- 
servation can  give  us  no  information  about  this,  since 
the  light  of  the  Aurora  is  never  sufficiently  intense  to 
be  visible  in  the  presence  of  daylight,  but  the  records 
of  the  magnetic  observatories  can  be,  and  have  been, 
appealed  to  for  information,  and  they  indicate  that 
the  facts  actually  accord  with  the  theory.  Behind 
the  veil  of  sunlight  in  the  middle  of  the  afternoon, 
there  is  good  reason  to  believe,  auroral  exhibitions 
often  take  place  which  would  eclipse  in  magnificence 
those  seen  at  night  if  we  could  behold  them.  Ob- 
servation shows,  too,  that  auroras  are  more  frequent 
before  than  after  midnight,  which  is  just  what  we 
should  expect  if  they  originate  in  the  way  that 
Arrhenius  supposes.  Second,  the  theory  offers  an  ex- 
planation of  the  alleged  fact  that  the  formation  of 
clouds  in  the  upper  air  is  more  frequent  in  years  when 
aurorae  are  most  abundant,  because  clouds  are  the 
result  of  the  condensation  of  moisture  upon  floating 
particles  in  the  atmosphere  (in  an  absolutely  dustless 
atmosphere  there  would  be  no  clouds),  and  it  has  been 

1 60 


proved  that  negative  ions  like  those  supposed  to  come 
from  the  sun  play  a  master  part  in  the  phenomena  of 
cloud  formation. 

Yet  another  singular  fact,  almost  mystical  in  its 
suggestions,  may  be  mentioned.  It  seems  that  the 
dance  of  the  auroral  lights  occurs  most  frequently 
during  the  absence  of  the  moon  from  the  hemisphere 
in  which  they  appear,  and  that  they  flee,  in  greater 
part,  to  the  opposite  hemisphere  when  the  moon's 
revolution  in  an  orbit  considerably  inclined  to  the 
earth's  equator  brings  her  into  that  where  they  have 
been  performing.  Arrhenius  himself  discovered  this 
curious  relation  of  auroral  frequency  to  the  position 
of  the  moon  north  or  south  of  the  equator,  and  he 
explains  it  in  this  way:  The  moon,  like  the  earth,  is 
exposed  to  the  influx  of  the  ions  from  the  sun;  but 
having  no  atmosphere,  or  almost  none,  to  interfere 
with  them,  they  descend  directly  upon  her  surface 
and  charge  her  with  an  electric  negative  potential  to  a 
very  high  degree.  In  consequence  of  this  she  affects 
the  electric  state  of  the  upper  parts  of  the  earth's 
atmosphere  where  they  lie  most  directly  beneath  her, 
and  thus  prevents,  to  a  large  extent,  the  negative 
discharges  to  which  the  appearance  of  the  Aurora  is 
due.  And  so  "the  extravagant  and  erring  spirit" 
of  the  Aurora  avoids  the  moon  as  Hamlet's  ghost 
fled  at  the  voice  of  the  cock  announcing  the  awakening 
of  the  god  of  day. 

There  are  even  other  apparent  confirmations 
of  the  hypothesis,  but  we  need  not  go  into  them. 
We  shall,  however,  find  one  more  application  of  it 
in  the  next  chapter,  for  it  appears  to  be  a  kind  of  cure- 



all  for  astronomical  troubles;  at  any  rate,  it  offers 
a  conceivable  solution  of  the  question,  How  does 
the  sun  manage  to  transmit  its  electric  influence  to 
the  earth  ?  And  this  solution  is  so  grandiose  in  con- 
ception, and  so  novel  in  the  mental  pictures  that  it 
offers,  that  its  acceptance  would  not  in  the  least  de- 
tract from  the  impression  that  the  Aurora  makes 
upon  the  imagination. 


THE  fears  and  legends  of  ancient  times  before 
Science  was  born,  and  the  superstitions  of  the 
Dark  Ages,  sedulously  cultivated  for  theological  pur- 
poses by  monks  and  priests,  have  so  colored  our  ideas 
of  the  influence  that  comets  have  had  upon  the 
human  mind  that  many  readers  may  be  surprised  to 
learn  that  it  was  the  apparition  of  a  wonderful  comet, 
that  of  1843,  which  led  to  the  foundation  of  our 
greatest  astronomical  institution,  the  Harvard  College 
Observatory.  No  doubt  the  comet  superstition  exist- 
ed half  a  century  ago,  as,  indeed,  it  exists  yet  to-day, 
but  in  this  case  the  marvellous  spectacle  in  the  sky 
proved  less  effective  in  inspiring  terror  than  in  awaken- 
ing a  desire  for  knowledge.  Even  in  the  sixteenth 
century  the  views  that  enlightened  minds  took  of 
comets  tended  powerfully  to  inspire  popular  con- 
fidence in  science,  and  Halley's  prediction,  after  seeing 
and  studying  the  motion  of  the  comet  which  ap- 
peared in  1682,  that  it  would  prove  to  be  a  regular 
member  of  the  sun's  family  and  would  be  seen  re- 
turning after  a  period  of  about  seventy-six  years,  to- 
gether with  the  fulfilment  of  that  prediction,  pro- 
duced a  revulsion  from  the  superstitious  notions 
which  had  so  long  prevailed. 



Then  the  facts  were  made  plain  that  comets  are 
subject  to  the  law  of  gravitation  equally  with  the 
planets;  that  there  are  many  which  regularly  return 
to  the  neighborhood  of  the  sun  (perihelion) ;  and  that 
these  travel  in  orbits  differing  from  those  of  the 
planets  only  in  their  greater  eccentricity,  alt  ough 
they  have  the  peculiarity  that  they  do  not,  like  the 
planets,  all  go  round  the  sun  in  the  same  direction, 
and  do  not  keep  within  the  general  plane  of  the 
planetary  system,  but  traverse  it  sometimes  from 
above  and  sometimes  from  below.  Other  comets, 
including  most  of  the  "  great "  ones,  appear  to  travel 
in  parabolic  or,  in  a  few  cases,  hyperbolic  orbits, 
which,  not  being  closed  curves,  never  bring  them  back 
again.  But  it  is  not  certain  that  these  orbits  may  not 
be  extremely  eccentric  ellipses,  and  that  after  the 
lapse  of  hundreds,  or  thousands,  of  years  the  comets 
that  follow  them  may  not  reappear.  The  question 
is  an  interesting  one,  because  if  all  orbits  are  really 
ellipses,  then  all  comets  must  be  permanent  members 
of  the  solar  system,  while  in  the  contrary  case  many 
of  them  are  simply  visitors,  seen  once  and  never  to 
be  seen  again.  The  hypothesis  that  comets  are 
originally  interlopers  might  seem  to  derive  some 
support  from  the  fact  that  the  certainly  periodic  ones 
are  associated,  in  groups,  with  the  great  outer  planets, 
whose  attraction  appears  to  have  served  as  a  trap 
for  them  by  turning  them  into  elliptical  orbits  and 
thus  making  them  prisoners  in  the  solar  system. 
Jupiter,  owing  to  his  great  mass  and  his  commanding 
situation  in  the  system,  is  the  chief  "comet-catcher"; 
but  he  catches  them  not  for  himself,  but  for  the  sun. 

1 66 



Yet  if  comets  do  come  originally  from  without  the 
borders  of  the  planetary  system,  it  does  not,  by  any 
means,  follow  that  they  were  wanderers  at  large  in 
space  before  they  yielded  to  the  overmastering  at- 
traction of  the  sun.  Investigation  of  the  known 
cometary  orbits,  combined  with  theoretical  con- 
siderations, has  led  some  astronomers  to  the  con- 
clusion that  as  the  sun  travels  onward  through  space 
he  ' '  picks  up  en  route ' '  cometary  masses  which,  with- 
out belonging  strictly  to  his  empire,  are  borne  along 
in  the  same  vast  "cosmical  current"  that  carries  the 
solar  system. 

But  while  no  intelligent  person  any  longer  thinks 
that  the  appearance  of  a  great  comet  is  a  token  from 
the  heavenly  powers  of  the  approaching  death  of  a 
mighty  ruler,  or  the  outbreak  of  a  devastating  war, 
or  the  infliction  of  a  terrible  plague  upon  wicked  man- 
kind, science  itself  has  discovered  mysteries  about 
comets  which  are  not  less  fascinating  because  they  are 
more  intellectual  than  the  irrational  fancies  that  they 
have  displaced.  To  bring  the  subject  properly  be- 
fore the  mind,  let  us  see  what  the  principal  phenomena 
connected  with  a  comet  are. 

At  the  present  day  comets  are  ordinarily  "picked 
up"  with  the  telescope  or  the  photographic  plate  be- 
fore any  one  except  their  discoverer  is  aware  of  their 
existence,  and  usually  they  remain  so  insignificant 
in  appearance  that  only  astronomers  ever  see  them. 
Yet  so  great  is  the  prestige  of  the  word  "comet" 
that  the  discovery  of  one  of  these  inconspicuous  wan- 
derers, and  its  subsequent  movements,  become  items 
of  the  day's  news  which  everybody  reads  with  the 



feeling,  perhaps,  that  at  least  he  knows  what  is  going 
on  in  the  universe  even  if  he  doesn't  understand  it. 
But  a  truly  great  comet  presents  quite  a  different  prop- 
osition. It,  too,  is  apt  to  be  detected  coming  out  of 
the  depths  of  space  before  the  world  at  large  can  get 
a  glimpse  of  it,  but  as  it  approaches  the  sun  its  aspect 
undergoes  a  marvellous  change.  Agitated  apparently 
by  solar  influence,  it  throws  out  a  long  streaming  tail 
of  nebulous  light,  directed  away  from  the  sun  and 
looking  as  if  blown  out  like  a  pennon  by  a  powerful 
wind.  Whatever  may  be  the  position  of  the  comet 
with  regard  to  the  sun,  as  it  circles  round  him  it  con- 
tinually keeps  its  tail  on  the  off  side.  This,  as  we  shall 
soon  see,  is  a  fact  of  capital  importance  in  relation  to 
the  probable  nature  of  comets'  tails.  Almost  at  the 
same  time  that  the  formation  of  the  tail  is  observed 
a  remarkable  change  takes  place  in  the  comet's  head, 
which,  by  the  way,  is  invariably  and  not  merely 
occasionally  its  most  important  part.  On  approach- 
ing the  sun  the  head  usually  contracts.  Coincidently 
with  this  contraction  a  nucleus  generally  makes  its 
appearance.  This  is  a  bright,  star-like  point  in  the 
head,  and  it  probably  represents  the  totality  of  solid 
matter  that  the  comet  possesses.  But  it  is  regarded 
as  extremely  unlikely  that  even  the  nucleus  consists 
of  a  uniformly  solid  mass.  If  it  were  such,  comets 
would  be  far  more  formidable  visitors  when  they  pass 
near  the  planets  than  they  have  'been  found  to  be. 
The  diameter  of  the  nucleus  may  vary  from  a  few 
hundred  up  to  several  thousand  miles;  the  heads,  on 
the  average,  are  from  twenty-five  thousand  to  one 
hundred  thousand  miles  in  diameter,  although  a  few 



have  greatly  exceeded  these  dimensions;  that  of  the 
comet  of  1811,  one  of  the  most  stupendous  ever  seen, 
was  a  million  and  a  quarter  miles  in  diameter !  As  to 
the  tails,  notwithstanding  their  enormous  length — 
some  have  been  more  than  a  hundred  million  miles 
long — there  is  reason  to  believe  that  they  are  of 
extreme  tenuity,  "as  rare  as  vacuum."  The  smallest 
stars  have  been  seen  shining  through  their  most 
brilliant  portions  with  undiminished  lustre. 

After  the  nucleus  has  been  formed  it  begins  to 
throw  out  bright  jets  directed  toward  the  sun.  A 
stream,  and  sometimes  several  streams,  of  light  also 
project  sunward  from  the  nucleus,  occasionally  ap- 
pearing like  a  stunted  tail  directed  oppositely  to  the 
real  tail.  Symmetrical  envelopes  which,  seen  in 
section,  appear  as  half  circles  or  parabolas,  rise  sun- 
ward from  the  nucleus,  forming  a  concentric  series. 
The  ends  of  these  stream  backward  into  the  tail,  to 
which  they  seem  to  supply  material.  Ordinarily  the 
formation  of  these  ejections  and  envelopes  is  attended 
by  intense  agitation  of  the  nucleus,  which  twists  and 
turns,  swinging  and  gyrating  with  an  appearance 
of  the  greatest  violence.  Sometimes  the  nucleus  is 
seen  to  break  up  into  several  parts.  The  entire  heads 
of  some  comets  have  been  split  asunder  in  passing 
close  around  the  sun;  the  comet  of  1882  retreated  into 
space  after  its  perihelion  passage  with  five  heads  in- 
stead of  the  one  that  it  had  originally,  and  each  of 
these  heads  had  its  own  tail! 

The  possession  of  the  spectroscope  has  enabled 
astronomers  during  later  years  to  study  the  chemical 
composition  of  comets  by  analyzing  their  light.  At 



first  the  only  substances  thus  discovered  in  them  were 
hydro-carbon  compounds,  due  evidently  to  the 
gaseous  envelopes  in  which  some  combination  of 
hydrogen  with  carbon  existed.  Behind  this  gaseous 
spectrum  was  found  a  faint  continuous  spectrum 
ascribed  to  the  nucleus,  which  apparently  both  re- 
flects the  sunlight  and  gives  forth  the  light  of  a  glow- 
ing solid  or  liquid.  Subsequently  sodium  and  iron 
lines  were  found  in  cometary  spectra.  The  presence 
of  iron  would  seem  to  indicate  that  some  of  these 
bodies  may  be  much  more  massive  than  observations 
on  their  attractive  effects  have  indicated.  In  some 
recent  comets,  such  as  Morehouse's,  in  1908,  several 
lines  have  been  found,  the  origin  of  which  is  unknown. 
Without  going  back  of  the  nineteenth  century  we 
may  find  records  of  some  of  the  most  extraordinary 
comets  that  man  has  ever  looked  upon.  In  1811, 
still  spoken  of  as  "the  year  of  the  comet,"  because  of 
the  wonderful  vintage  ascribed  to  the  skyey  visitor,  a 
comet  shaped  like  a  gigantic  sword  amazed  the  whole 
world,  and, as  it  remained  visible  for  seventeen  months, 
was  regarded  by  superstitious  persons  as  a  symbol 
of  the  fearful  happenings  of  Napoleon's  Russian 
campaign.  This  comet,  the  extraordinary  size  of 
whose  head,  greatly  exceeding  that  of  the  sun  itself, 
has  already  been  mentioned,  was  also  remarkable  for 
exhibiting  so  great  a  brilliancy  without  approaching 
even  to  the  earth's  distance  from  the  sun.  But  there 
was  once  a  comet  (and  only  once — in  the  year  1729) 
which  never  got  nearer  to  the  sun  than  four  times  the 
distance  of  the  earth  and  yet  appeared  as  a  formid- 
able object  in  the  sky.  As  Professor  Young  has  re- 



marked,  "it  must  have  been  an  enormous  comet  to 
be  visible  from  such  a  distance."  And  we  are  to 
remember  that  there  were  no  great  telescopes  in  the 
year  1729.  That  comet  affects  the  imagination  like 
a  phantom  of  space  peering  into  the  solar  system,  dis- 
playing its  enormous  train  afar  off  (which,  if  it  had 
approached  as  near  as  other  comets,  would  probably 
have  become  the  celestial  wonder  of  all  human 
memory),  and  then  turning  away  and  vanishing  in  the 
depths  of  immensity. 

In  1843  a  comet  appeared  which  was  so  brilliant 
that  it  could  be  seen  in  broad  day  close  beside  the 
sun!  This  was  the  first  authenticated  instance  of 
that  kind,  but  the  occurrence  was  to  be  repeated,  as 
we  shall  see  in  a  moment,  less  than  forty  years  later. 

The  splendid  comet  of  1858,  usually  called  Donati's, 
is  remembered  by  many  persons  yet  living.  It  was, 
perhaps,  both  as  seen  by  the  naked  eye  and  with  the 
telescope,  the  most  beautiful  comet  of  which  we  have 
any  record.  It  too  marked  a  rich  vintage  year,  still 
remembered  in  the  vineyards  of  France,  where  there 
is  a  popular  belief  that  a  great  comet  ripens  the  grape 
and  imparts  to  the  wine  a  flavor  not  attainable  by 
the  mere  skill  of  the  cultivator.  There  are  "  comet 
wines,"  carefully  treasured  in  certain  cellars,  and 
brought  forth  only  when  their  owner  wishes  to  treat 
his  guests  to  a  sip  from  paradise. 

The  year  1861  saw  another  very  remarkable  comet, 
of  an  aspect  strangely  vast  and  diffuse,  which  is 
believed  to  have  swept  the  earth  with  its  immense 
tail  when  it  passed  between  us  and  the  sun  on  the 
night  of  June  3oth,  an  event  which  produced  no  other 


known  effect  than  the  appearance  of  an  unwonted 
amount  of  scattered  light  in  the  sky. 

The  next  very  notable  comet  was  the  "Great 
Southern  Comet"  of  1880,  which  was  not  seen  from 
the  northern  hemisphere.  It  mimicked  the  aspect 
of  the  famous  comet  of  1843,  and  to  the  great  sur- 
prise of  astronomers  appeared  to  be  travelling  in  the 
same  path.  This  proved  to  be  the  rising  of  the 
curtain  for  an  astronomical  sensation  unparalleled  in 
its  kind;  for  two  years  later  another  brilliant  comet 
appeared,  first  in  the  southern  hemisphere,  and  it  too 
followed  the  same  track.  The  startling  suggestion  was 
now  made  that  this  comet  was  identical  with  those 
of  1843  and  1880,  its  return  having  been  hastened  by 
the  resistance  experienced  in  passing  twice  through  the 
coronal  envelope,  and  there  were  some  who  thought 
that  it  would  now  swing  swiftly  round  and  then 
plunge  straight  into  the  sun,  with  consequences  that 
might  be  disastrous  to  us  on  account  of  the  "flash 
of  heat"  that  would  be  produced  by  the  impact. 
Nervous  people  were  frightened,  but  observation  soon 
proved  that  the  danger  was  imaginary,  for  although 
the  comet  almost  grazed  the  sun,  and  must  have 
rushed  through  two  or  three  million  miles  of  the 
coronal  region,  no  retardation  of  its  immense  velocity 
was  perceptible,  and  it  finally  passed  away  in  a 
damaged  condition,  as  before  remarked,  and  has  never 
since  appeared. 

Then  the  probable  truth  was  perceived — viz.,  that 
the  three  comets  (1843,  1880,  and  1882)  were  not 
one  identical  body,  but  three  separate  ones  all  travel- 
ling in  the  same  orbit.  It  was  found,  too,  that  a 


comet  seen  in  1668  bore  similar  insignia  of  relation- 
ship. The  natural  inference  was  that  these  four 
bodies  had  once  formed  a  single  mass  which  had 
been  split  apart  by  the  disruptive  action  of  the  sun. 
Strength  was  lent  to  this  hypothesis  by  the  fact  that 
the  comet  of  1882  was  apparently  torn  asunder  dur- 
ing its  perihelion  passage,  retreating  into  space  in  a 
dissevered  state.  But  Prof.  George  Forbes  has  a 
theory  that  the  splitting  of  the  original  comet ary  mass 
was  effected  by  an  unknown  planet,  probably  greater 
than  Jupiter,  situated  at  a  hundred  times  the  earth's 
distance  from  the  sun,  and  revolving  in  a  period  of  a 
thousand  years.  He  supposes  that  the  original  comet 
was  not  that  of  1668,  but  one  seen  in  1556,  which  has 
since  been  "missing,"  and  that  its  disruption  occurred 
from  an  encounter  with  the  supposititious  planet 
about  the  year  1700.  Truly  from  every  point  of  view 
comets  are  the  most  extraordinary  of  adventurers! 

The  comet  of  1882  was  likewise  remarkable  for 
being  visible,  like  its  predecessor  of  1843,  m  fall  day- 
light  in  close  proximity  to  the  sun.  The  story  of  its 
detection  when  almost  in  contact  with  the  solar  disk 
is  dramatic.  It  had  been  discovered  in  the  southern 
hemisphere  only  a  couple  of  weeks  before  its  perihelion, 
which  occurred  on  September  i7th,  and  on  the  fore- 
noon of  that  day  it  was  seen  by  Doctor  Common  in 
England,  and  by  Doctor  Elkin  and  Mr.  Finlay  at  the 
Cape  of  Good  Hope,  almost  touching  the  sun.  It 
looked  like  a  dazzling  white  bird  with  outspread 
wings.  The  southern  observers  watched  it  go  right 
into  the  sun,  when  it  instantly  disappeared.  What 
had  happened  was  that  the  comet  in  passing  its 


perihelion  point  had  swung  exactly  between  the  earth 
and  the  sun.  On  the  following  morning  it  was  seen 
from  all  parts  of  the  world  close  by  the  sun  on  the 
opposite  side,  and  it  remained  thus  visible  for  three 
days,  gradually  receding  from  the  solar  disk.  It  then 
became  visible  for  northern  observers  in  the  morning 
sky  before  sunrise,  brandishing  a  portentous  sword- 
shaped  tail  which,  if  it  had  been  in  the  evening  sky, 
would  have  excited  the  wonder  of  hundreds  of  millions, 
but  situated  where  it  was,  comparatively  few  ever  saw  it. 
The  application  of  photography  to  the  study  of 
comets  has  revealed  many  curious  details  which 
might  otherwise  have  escaped  detection,  or  at  best 
have  remained  subject  to  doubt.  It  has  in  particular 
shown  not  only  the  precise  form  of  the  tails,  but  the 
remarkable  vicissitudes  that  they  undergo.  Professor 
Barnard's  photographs  of  Brooks'  comet  in  1893 
suggested,  by  the  extraordinary  changes  in  the  form 
of  the  tail  which  they  revealed,  that  the  comet  was 
encountering  a  series  of  obstructions  in  space  which 
bent  and  twisted  its  tail  into  fantastic  shapes.  The 
reader  will  observe  the  strange  form  into  which  the 
tail  was  thrown  on  the  night  of  October  2ist.  A 
cloud  of  meteors  through  which  the  comet  was  passing 
might  have  produced  such  deformations  of  its  tail. 
In  the  photograph  of  Daniels'  comet  of  1907,  a  curious 
striping  of  the  tail  will  be  noticed.  The  short  bright 
streaks  seen  in  the  photograph,  it  may  be  explained, 
are  the  images  of  stars  which  are  drawn  out  into  lines 
in  consequence  of  the  fact  that  the  photographic 
telescope  was  adjusted  to  follow  the  motion  of  the 
comet  while  the  stars  remained  at  rest. 


DANIELS      COMET.       AUGUST    II,    1907 


But  the  adventures  of  comets  are  not  confined  to 
possible  encounters  with  unknown  obstacles.  We 
have  referred  to  the  fact  that  the  great  planets,  and 
especially  Jupiter,  frequently  interfere  with  the 
motions  of  comets.  This  interference  is  not  limited  to 
the  original  alteration  of  their  orbits  from  possible 
parabolas  to  ellipses,  but  is  sometimes  exercised  again 
and  again,  turning  the  bewildered  comets  into 
elliptical  paths  of  all  degrees  of  eccentricity.  A 
famous  example  of  this  kind  of  planetary  horse-play 
is  furnished  by  the  story  of  LexelFs  missing  comet. 
This  comet  was  first  seen  in  1770.  Investigation 
showed  that  it  was  moving  in  an  orbit  which  should 
bring  it  back  to  perihelion  every  five  and  a  half  years ; 
yet  it  had  never  been  seen  before  and,  although  often 
searched  for,  has  never  been  seen  since.  Laplace  and 
Leverrier  proved  mathematically  that  in  1767  it 
had  approached  so  close  to  Jupiter  as  to  be  involved 
among  the  orbits  of  his  satellites.  What  its  track 
had  been  before  is  not  known,  but  on  that  occasion  the 
giant  planet  seized  the  interloper,  threw  it  into  a  short 
elliptic  orbit,  and  sent  it,  like  an  arrested  vagrant,  to 
receive  sentence  at  the  bar  of  the  sun.  On  this 
journey  it  passed  within  less  than  1,500,000  miles  of 
the  earth.  The  form  of  orbit  which  Jupiter  had  im- 
pressed required,  as  we  have  said,  its  return  in  about 
five  and  a  half  years;  but  soon  after  1770  it  had  the 
misfortune  a  second  time  to  encounter  Jupiter  at 
close  range,  and  he,  as  if  dissatisfied  with  the  leniency 
of  the  sun,  or  indignant  at  the  stranger's  familiarity, 
seized  the  comet  and  hurled  it  out  of  the  system,  or 
at  any  rate  so  far  away  that  it  has  never  since  been 



able  to  rejoin  the  family  circle  that  basks  in  trn 
immediate  rays  of  the  solar  hearth.  Nor  is  this  the 
only  instance  in  which  Jupiter  has  dealt  summarily 
with  small  comets  that  have  approached  him  with 
too  little  deference. 

The  function  which  Jupiter  so  conspicuously  ful- 
fils as  master  of  the  hounds  to  the  sun  is  worth  con- 
sidering a  little  more  in  detail.  To  change  the  figure, 
imagine  the  sun  in  its  voyage  through  space  to  be 
like  a  majestic  battleship  surrounded  by  its  scouts. 
Small  vessels  (the  comets),  as  they  are  overhauled 
by  the  squadron,  are  taken  in  charge  by  the  scouts, 
with  Jupiter  for  their  chief,  and  are  forced  to  accom- 
pany the  fleet;  but  not  all  are  impressed.  If  a  strange 
comet  undertakes  to  run  across  Jupiter's  bows  the 
latter  brings  it  to,  and  makes  prize  of  it  by  throwing 
it  into  a  relatively  small  ellipse  with  the  sun  for  its 
focus.  Thenceforth,  unless,  as  happened  to  the  un- 
happy comet  of  Lexell,  it  encounters  Jupiter  again 
in  such  a  way  as  to  be  diverted  by  him  into  a  more 
distant  orbit,  it  can  never  get  away.  About  thirty 
comets  are  now  known  to  have  thus  been  captured 
by  the  great  planet,  and  they  are  called  "Jupiter's 
Comet  Family."  But,  on  the  other  hand,  if  a  wan- 
dering comet  crosses  the  wake  of  the  chief  planetary 
scout  the  latter  simply  drives  it  away  by  accelerating 
its  motion  and  compels  it  to  steer  off  into  open  space. 
The  transformation  of  comets  into  meteors  will  be 
considered  in  the  next  chapter,  but  here,  in  passing, 
mention  may  be  made  of  the  strange  fate  of  one  mem- 
ber of  Jupiter's  family,  Biela's  comet,  which,  having 
become  overbold  in  its  advances  to  its  captor,  was, 

i  So 


after  a  few  revolutions  in  its  impressed  orbit,  torn  to 
pieces  and  turned  into  a  flock  of  meteors. 

And  now  let  us  return  to  the  mystery  of  comets' 
tails.  That  we  are  fully  justified  in  speaking  of  the 
tails  of  comets  as  mysterious  is  proved  by  the  dec- 
laration of  Sir  John  Herschel,  who  averred,  in  so 
many  words,  that  "there  is  some  profound  secret  and 
mystery  of  nature  concerned  in  this  phenomenon," 
and  this  profound  secret  and  mystery  has  not  yet  been 
altogether  cleared  up.  Nevertheless,  the  all-explain- 
ing hypothesis  of  Arrhenius  offers  us  once  more  a 
certain  amount  of  aid.  Comets'  tails,  Arrhenius 
assures  us,  are  but  another  result  of  the  pressure  of 
light.  The  reader  will  recall  the  applications  of  this 
theory  to  the  Zodiacal  Light  and  the  Aurora.  In  the 
form  in  which  we  now  have  to  deal  with  it,  the  sup- 
position is  made  that  as  a  comet  approaches  the  sun 
eruptions  of  vapor,  due  to  the  solar  heat,  occur  in  its 
nucleus.  These  are  naturally  most  active  on  the 
side  which  is  directly  exposed  to  the  sun,  whence  the 
appearance  of  the  immense  glowing  envelopes  that 
surround  the  nucleus  on  the  sunward  side.  Among  the 
particles  of  hydro-carbon,  and  perhaps  solid  carbon 
in  the  state  of  fine  dust,  which  are  thus  set  free  there 
will  be  many  whose  size  is  within  the  critical  limit 
which  enables  the  light-waves  from  the  sun  to  drive 
them  away.  Clouds  of  such  particles,  then,  will 
stream  off  behind  the  advancing  comet,  producing  the 
appearance  of  a  tail.  This  accounts  for  the  fact  that 
the  tails  of  comets  are  always  directed  away  from 
the  sun,  and  it  also  explains  the  varying  forms  of  the 
tails  and  the  extraordinary  changes  that  they  undergo. 

xo  183 


The  speed  of  the  particles  driven  before  the  light- 
waves must  depend  upon  their  size  and  weight,  the 
lightest  of  a  given  size  travelling  the  most  swiftly. 
By  accretion  certain  particles  might  grow,  thus  losing 
velocity  and  producing  the  appearance  of  bunches 
in  the  tail,  such  as  have  been  observed.  The  hypoth- 
esis also  falls  in  with  the  researches  of  Bredichin, 
who  has  divided  the  tails  of  comets  into  three  principal 
classes — viz.:  (i)  Those  which  appear  as  long,  straight 
rays;  (2)  Those  which  have  the  form  of  curved  plumes 
or  scimitars;  (3)  Those  which  are  short,  brushy,  and 
curved  sharply  backward  along  the  comet's  path. 
In  the  first  type  he  calculates  the  repulsive  force  at 
from  twelve  to  fifteen  times  the  force  of  gravity;  in 
the  second  at  from  two  to  four  times;  and  in  the 
third  at  about  one  and  a  half  times.  The  straight 
tails  he  ascribes  to  hydrogen  because  the  hydrogen 
atom  is  the  lightest  known;  the  sword-shaped  tails 
to  hydro-carbons;  and  the  stumpy  tails  to  vaporized 
iron.  It  will  be  seen  that,  if  the  force  driving  off  the 
tails  is  that  which  Arrhenius  assumes  it  to  be,  the 
forms  of  those  appendages  would  accord  with  those 
that  Bredichin 's  theory  calls  for.  At  the  same  time 
we  have  an  explanation  of  the  multiple  tails  with  which 
some  comets  have  adorned  themselves.  The  comet 
of  1744,  for  instance,  had  at  one  time  no  less  than 
seven  tails  spread  in  a  wide  curved  brush  behind  it. 
Donati's  comet  of  1858  also  had  at  least  two  tails, 
the  principal  one  sword-shaped  and  the  other  long, 
narrow,  and  as  straight  as  a  rule.  According  to  Bred- 
ichin, the  straight  tail  must  have  been  composed  of 
hydrogen,  and  the  other  of  some  form  of  hydro-carbon 



whose  atoms  are  heavier  than  those  of  hydrogen,  and, 
consequently,  when  swept  away  by  the  storm  of  light- 
waves, followed  a  curvature  depending  upon  the 
resultant  of  the  forces  operating  upon  them.  The 
seven  tails  of  the  comet  of  1744  presented  a  kind  of 
diagram  graphically  exhibiting  its  complex  composi- 
tion, and,  if  we  knew  a  little  more  about  the  con- 
stituents of  a  comet,  we  might  be  able  to  say  from 
the  amount  of  curvature  of  the  different  tails  just 
what  were  the  seven  substances  of  which  that  comet 

If  these  theories  seem  to  the  reader  fantastic,  at 
any  rate  they  are  no  more  fantastic  than  the  phenom- 
ena that  they  seek  to  explain. 



ONE  of  the  most  terrorizing  spectacles  with  which 
the  heavens  have  ever  caused  the  hearts  of  men 
to  quake  occurred  on  the  night  of  November  13,  1833. 
On  that  night  North  America,  which  faced  the  storm, 
was  under  a  continual  rain  of  fire  from  about  ten 
o'clock  in  the  evening  until  daybreak. 

The  fragments  of  a  comet  had  struck  the  earth. 

But  the  meaning  of  what  had  happened  was  not 
discovered  until  long  afterward.  To  the  astronomers 
who,  with  astonishment  not  less  than  that  of  other 
people,  watched  the  wonderful  scene,  it  was  an  un- 
paralleled "shower  of  meteors."  They  did  not  then 
suspect  that  those  meteors  had  once  formed  the  head 
of  a  comet.  Light  dawned  when,  a  year  later,  Prof. 
Denison  Olmstead,  of  Yale  College,  demonstrated  that 
the  meteors  had  all  moved  in  parallel  orbits  around 
the  sun,  and  that  these  orbits  intersected  that  of  the 
earth  at  the  point  where  our  planet  happened  to  be 
on  the  memorable  night  of  November  i3th.  Professor 
Olmstead  even  went  so  far  as  to  suggest  that  the 
cloud  of  meteors  that  had  encountered  the  earth 
might  form  a  diffuse  comet ;  but  full  recognition  of  the 
fact  that  they  were  cometary  debris  came  later,  as 



the  result  of  further  investigation.  The  key  to  the 
secret  was  plainly  displayed  in  the  spectacle  itself, 
and  was  noticed  without  being  understood  by  thou- 
sands of  the  terror-stricken  beholders.  It  was  an 
umbrella  of  fire  that  had  opened  overhead  and  covered 
the  heavens ;  in  other  words,  the  meteors  all  radiated 
from  a  particular  point  in  the  constellation  Leo,  and, 
being  countless  as  the  snowflakes  in  a  winter  tempest, 
they  ribbed  the  sky  with  fiery  streaks.  Professor 
Olmstead  showed  that  the  radiation  of  the  meteors 
from  a  fixed  point  was  an  effect  of  perspective,  and 
in  itself  a  proof  that  they  were  moving  in  parallel 
paths  when  they  encountered  the  earth.  The  fact 
was  noted  that  there  had  been  a  similar,  but  in- 
comparably less  brilliant,  display  of  meteors  on  the 
same  day  of  November,  1832,  and  it  was  rightly  con- 
cluded that  these  had  belonged  to  the  same  stream, 
although  the  true  relationship  of  the  phenomena  was 
not  immediately  apprehended.  Olmstead  ascribed 
to  the  meteors  a  revolution  about  the  sun  once  in 
every  six  months,  bringing  them  to  the  intersection 
of  their  orbit  with  that  of  the  earth  every  November 
1 3th;  but  later  investigators  found  that  the  real 
period  was  about  thirty-three  and  one-quarter  years, 
so  that  the  great  displays  were  due  three  times  in  a 
century,  and  their  return  was  confidently  predicted 
for  the  year  1866.  The  appearance  of  the  meteors 
in  1832,  a  year  before  the  great  display,  was  ascribed 
to  the  great  length  of  the  stream  which  they  formed 
in  space — so  great  that  they  required  more  than  two 
years  to  cross  the  earth's  orbit.  In  1832  the  earth  had 
encountered  a  relatively  rare  part  of  the  stream, 



but  in  1833,  on  returning  to  the  crossing-place,  it 
found  there  the  richest  part  of  the  stream  pouring 
across  its  orbit.  This  explanation  also  proved  to  be 
correct,  and  the  predicted  return  in  1866  was  duly 
witnessed,  although  the  display  was  much  less  brilliant 
than  in  1833.  It  was  followed  by  another  in  1867. 

In  the  mean  time  Olmstead's  idea  of  a  cometary 
relationship  of  the  meteors  was  demonstrated  to  be 
correct  by  the  researches  of  Schiaparelli  and  others, 
who  showed  that  not  only  the  November  meteors,  but 
those  of  August,  which  are  seen  more  or  less  abun- 
dantly every  year,  travelled  in  the  tracks  of  well- 
known  comets,  and  had  undoubtedly  an  identical 
origin  with  those  comets.  In  other  words  the  comets 
and  the  meteor-swarms  were  both  remnants  of  original 
masses  which  had  probably  been  split  up  by  the  action 
of  the  sun,  or  of  some  planet  to  which  they  had  made 
close  approaches.  The  annual  periodicity  of  the 
August  meteors  was  ascribed  to  the  fact  that  the 
separation  had  taken  place  so  long  ago  that  the 
meteors  had  become  distributed  all  around  the  orbit, 
in  consequence  of  which  the  earth  encountered 
some  of  them  every  year  when  it  arrived  at  the 
crossing  -  point.  Then  Leverrier  showed  that  the 
original  comet  associated  with  the  November  meteors 
was  probably  brought  into  the  system  by  the  influence 
of  the  planet  Uranus  in  the  year  126  of  the  Christian 
era.  Afterward  Alexander  Herschel  identified  the 
tracks  of  no  less  than  seventy-six  meteor  -  swarms 
(most  of  them  inconspicuous)  with  those  of  comets. 
The  still  more  recent  researches  of  Mr.  W.  F.  Denning 
make  it  probable  that  there  are  no  meteors  which 



„  p*o 

3  »  c^ 


O   CO    m 

0  3 

3-33     H 
<D  g  01    W 

f  f!  § 

t1  3  5*    H 






do  not  belong  to  a  flock  or  system  probably  formed 
by  the  disintegration  of  a  cometary  mass;  even  the 
apparently  sporadic  ones  which  shoot  across  the  sky, 
"lost  souls  in  the  night,"  being  members  of  flocks 
which  have  become  so  widely  scattered  that  the  earth 
sometimes  takes  weeks  to  pass  through  the  region  of 
space  where  their  paths  lie. 

The  November  meteors  should  have  exhibited  an- 
other pair  of  spectacles  in  1899  and  1900,  and  their 
failure  to  do  so  caused  at  first  much  disappointment, 
until  it  was  made  plain  that  a  good  reason  existed 
for  their  absence.  It  was  found  that  after  their  last 
appearance,  in  1867,  they  had  been  disturbed  in  their 
movements  by  the  planets  Jupiter  and  Saturn,  whose 
attractions  had  so  shifted  the  position  of  their  orbit 
that  it  no  longer  intersected  that  of  the  earth,  as  it 
did  before.  Whether  another  planetary  interference 
will  some  time  bring  the  principal  mass  of  the  Novem- 
ber meteors  back  to  the  former  point  of  intersection 
with  the  earth's  orbit  is  a  question  for  the  future  to 
decide.  It  would  seem  that  there  may  be  several 
parallel  streams  of  the  November  meteors,  and  that 
some  of  them,  like  those  of  August,  are  distributed 
entirely  around  the  orbit,  so  that  every  mid-November 
we  see  a  few  of  them. 

We  come  now  to  a  very  remarkable  example  of  the 
disintegration  of  a  comet  and  the  formation  of  a 
meteor  -  stream.  In  1826  Biela,  of  Josephstadt, 
Austria,  discovered  a  comet  to  which  his  name  was 
given.  Calculation  showed  that  it  had  an  orbital 
period  of  about  six  and  a  half  years,  belonging  to 
Jupiter's  "family."  On  one  of  its  returns,  in  1846, 



it  astonished  its  watchers  by  suddenly  splitting  in  two. 
The  two  comets  thus  formed  out  of  one  separated  to 
a  distance  of  about  one  hundred  and  sixty  thousand 
miles,  and  then  raced  side  by  side,  sometimes  with  a 
curious  ligature  connecting  them,  like  Siamese  twins, 
until  they  disappeared  together  in  interplanetary 
space.  In  1852  they  came  back,  still  nearly  side  by 
side;  but  now  the  distance  between  them  had  in- 
creased to  a  million  and  a  quarter  of  miles.  After 
that,  at  every  recurrence  of  their  period,  astronomers 
looked  for  them  in  vain,  until  1872,  when  an  amazing 
thing  happened.  On  the  night  of  November  28th, 
when  the  earth  was  crossing  the  plane  of  the  orbit  of 
the  missing  comet,  a  brilliant  shower  of  meteors 
burst  from  the  northern  sky,  travelling  nearly  in  the 
track  which  the  comet  should  have  pursued.  The 
astronomers  were  electrified.  Klinkerfues,  of  Gottin- 
gen,  telegraphed  to  Pogson,  of  Madras:  "Biela  touched 
earth;  search  near  Theta  Centauri"  Pogson  searched 
in  the  place  indicated  and  saw  a  cometary  mass  re- 
treating into  the  southern  heavens,  where  it  was  soon 
swallowed  from  sight! 

Since  then  the  Biela  meteors  have  been  among  the 
recognized  periodic  spectacles  of  the  sky,  and  few  if 
any  doubt  that  they  represent  a  portion  of  the  missing 
comet  whose  disintegration  began  with  the  separation 
into  two  parts  in  1846.  The  comet  itself  has  never 
since  been  seen.  The  first  display  of  these  meteors, 
sometimes  called  the  "Andromedes,"  because  they 
radiate  from  the  constellation  Andromeda,  was  re- 
markable for  the  great  brilliancy  of  many  of  the  fire- 
balls that  shot  among  the  shower  of  smaller  sparks, 



Showing  the  mean  elevation  at 
which  meteorites  and  meteors  make 
their  appearance.  Below  are  shown 
the  elevation  of  Mount  Everest;  the 
.highest  manned  balloon  ascent  by 
M.  Berson;  the  height  of  cirrus  clouds; 
the  highest  free  balloon  ascent;  and 
the  elevation  attained  by  the  clouds 
^of  fire-dust  ejected  by  the  Krakatoa 
eruption  in  1883.  (From  La  Nature.) 


some  of  which  were  described  as  equalling  the  full 
moon  in  size.  None  of  them  is  known  to  have  reached 
the  earth,  but  during  the  display  of  the  same  meteors 
in  1885  a  meteoric  mass  fell  at  Mazapil  in  Northern 
Mexico  (it  is  now  in  the  Museum  at  Vienna),  which 
many  have  thought  may  actually  be  a  piece  of  the 
original  comet  of  Biela.  This  brings  us  to  the  second 
branch  of  our  subject. 

More  rare  than  meteors  or  falling  stars,  and  more 
startling,  except  that  they  never  appear  in  showers, 
are  the  huge  balls  of  fire  which  occasionally  dart 
through  the  sky,  lighting  up  the  landscapes  beneath 
with  their  glare,  leaving  trains  of  sparks  behind  them, 
often  producing  peals  of  thunder  when  they  explode, 
and  in  many  cases  falling  upon  the  earth  and  burying 
themselves  from  a  few  inches  to  several  feet  in  the 
soil,  from  which,  more  than  once,  they  have  been 
picked  up  while  yet  hot  and  fuming.  These  balls 
are  sometimes  called  bolides.  They  are  not  really 
round  in  shape,  although  they  often  look  so  while 
traversing  the  sky,  but  their  forms  are  fragmentary, 
and  occasionally  fantastic.  It  has  been  supposed 
that  their  origin  is  different  from  that  of  the  true 
meteors ;  it  has  even  been  conjectured  that  they  may 
have  originated  from  the  giant  volcanoes  of  the  moon 
or  have  been  shot  out  from  the  sun  during  some  of  the 
tremendous  explosions  that  accompany  the  formation 
of  eruptive  prominences.  By  the  same  reasoning 
some  of  them  might  be  supposed  to  have  come  from 
some  distant  star.  Others  have  conjectured  that  they 
are  wanderers  in  space,  of  unknown  origin,  which  the 
earth  encounters  as  it  journeys  on,  and  Lord  Kelvin 


made  a  suggestion  which  has  become  classic  because 
of  its  imaginative  reach — viz.,  that  the  first  germs  of 
life  may  have  been  brought  to  the  earth  by  one  of 
these  bodies,  "a  fragment  of  an  exploded  world." 

It  is  a  singular  fact  that  astronomers  and  scien- 
tific men  in  general  were  among  the  last  to  admit 
the  possibility  of  solid  masses  falling  from  the  sky. 
The  people  had  believed  in  the  reality  of  such  phenom- 
ena from  the  earliest  times,  but  the  savants  shook 
their  heads  and  talked  of  superstition.  This  was  the 
less  surprising  because  no  scientifically  authenticated 
instance  of  such  an  occurrence  was  known,  and  the 
stones  popularly  believed  to  have  fallen  from  the  sky 
had  become  the  objects  of  worship  or  superstitious 
reverence,  a  fact  not  calculated  to  recommend  them 
to  scientific  credence.  The  celebrated  "black  stone" 
suspended  in  the  Kaaba  at  Mecca  is  one  of  these 
reputed  gifts  from  heaven;  the  "Palladium  "  of  ancient 
Troy  was  another;  and  a  stone  which  fell  near  En- 
sisheim,  in  Germany,  was  placed  in  a  church  as  an 
object  to  be  religiously  venerated.  Many  legends  of 
falling  stones  existed  in  antiquity,  some  of  them  curi- 
ously transfigured  by  the  imagination,  like  the  "Lion 
of  the  Peloponnesus,"  which  was  said  to  have  sprung 
down  from  the  sky  upon  the  Isthmus  of  Corinth.  But 
near  the  beginning  of  the  nineteenth  century,  in  1803, 
a  veritable  shower  of  falling  stones  occurred  at  L'Aigle, 
in  Northern  France,  and  this  time  astronomers  took 
note  of  the  phenomenon  and  scientifically  investigated 
it.  Thousands  of  the  strange  projectiles  came  from 
the  sky  on  this  occasion,  and  were  scattered  over  a 
wide  area  of  country,  and  some  buildings  were  hit. 



Four  years  later  another  shower  of  stones  occurred  at 
Weston,  Conn.,  numbering  thousands  of  individuals. 
The  local  alarm  created  in  both  cases  was  great,  as 
well  it  might  be,  for  what  could  be  more  intimidating 
than  to  find  the  blue  vault  of  heaven  suddenly  hurling 
solid  missiles  at  the  homes  of  men?  After  these 
occurrences  it  was  impossible  for  the  most  skeptical 
to  doubt  any  longer,  and  the  regular  study  of  "aero- 
lites," or  "meteorites,"  began. 

One  of  the  first  things  recognized  was  the  fact  that 
fire-balls  are  solid  meteorites  in  flight,  and  not  gaseous 
exhalations  in  the  air,  as  some  had  assumed.  They 
burn  in  the  air  during  their  flight,  and  sometimes,  per- 
haps, are  entirely  consumed  before  reaching  the 
ground.  Their  velocity  before  entering  the  earth's 
atmosphere  is  equal  to  that  of  the  planets  in  their 
orbits — viz.,  from  twenty  to  thirty  miles  per  second — 
a  fact  which  proves  that  the  sun  is  the  seat  of  the 
central  force  governing  them.  Their  burning  in  the 
air  is  not  difficult  to  explain;  it  is  the  heat  of  friction 
which  so  quickly  brings  them  to  incandescence.  Cal- 
culation shows  that  a  body  moving  through  the  air 
at  a  velocity  of  about  a  mile  per  second  will  be  brought, 
superficially,  to  the  temperature  of  "red  heat"  by 
friction  with  the  atmosphere.  If  its  velocity  is  twenty 
miles  per  second  the  temperature  will  become  thou- 
sands of  degrees.  This  is  the  state  of  affairs  with  a 
meteorite  rushing  into  the  earth's  atmosphere;  its 
surface  is  liquefied  within  a  few  seconds  after  the 
friction  begins  to  act,  and  the  melted  and  vaporized 
portion  of  its  mass  is  swept  backward,  forming  the 
train  of  sparks  that  follows  every  great  fire-ball,  How- 



ever,  there  is  one  phenomenon  connected  with  the 
trains  of  meteorites  which  has  never  been  satisfac- 
torily explained:  they  often  persist  for  long  periods 
of  time,  drifting  and  turning  with  the  wind,  but  not 
ceasing  to  glow  with  a  phosphorescent  luminosity. 
The  question  is,  Whence  comes  this  light?  It  must 
be  light  without  heat,  since  the  fine  dust  or  vapor 
of  which  the  train  can  only  consist  would  not  retain 
sufficient  heat  to  render  it  luminous  for  so  long  a  time. 
An  extremely  remarkable  incident  of  this  kind  oc- 
curred on  February  22,  1909,  when  an  immense  fire- 
ball that  passed  over  southern  England  left  a  train 
that  remained  visible  during  two  hours,  assuming 
many  curious  shapes  as  it  was  drifted  about  by  cur- 
rents in  the  air. 

But  notwithstanding  the  enormous  velocity  with 
which  meteorites  enter  the  air  they  are  soon  slowed 
down  to  comparatively  moderate  speed,  so  that  when 
they  disappear  they  are  usually  travelling  not  faster 
than  a  mile  a  second.  The  courses  of  many  have  been 
traced  by  observers  situated  along  their  track  at 
various  points,  and  thus  a  knowledge  has  been  ob- 
tained of  their  height  above  the  ground  during  their 
flight  and  of  the  length  of  their  visible  courses.  They 
generally  appear  at  an  elevation  of  eighty  or  a  hun- 
dred miles,  and  are  seldom  visible  after  having  de- 
scended to  within  five  miles  of  the  ground,  unless  the 
observer  happens  to  be  near  the  striking-point,  when 
he  may  actually  witness  the  fall.  Frequently  they 
burst  while  high  in  the  air  and  their  fragments  are 
scattered  like  shrapnel  over  the  surface  of  the  ground, 
sometimes  covering  an  area  of  several  square  miles, 




but  of  course  not  thickly;  different  fragments  of  the 
same  meteorite  may  reach  the  ground  at  points  several 
miles  apart.  The  observed  length  of  their  courses  in 
the  atmosphere  varies  from  fifty  to  five  hundred 
miles.  If  they  continued  a  long  time  in  flight  after 
entering  the  air,  even  the  largest  of  them  would  prob- 
ably be  consumed  to  the  last  scrap,  but  their  fiery 
career  is  so  short  on  account  of  their  great  speed  that 
the  heat  does  not  have  time  to  penetrate  very  deeply, 
and  some  that  have  been  picked  up  immediately  after 
their  fall  have  been  found  cold  as  ice  within.  Their 
size  after  reaching  the  ground  is  variable  within  wide 
limits ;  some  are  known  which  weigh  several  tons,  but 
the  great  majority  weigh  only  a  few  pounds  and  many 
only  a  few  ounces. 

Meteorites  are  of  two  kinds:  stony  meteorites  and 
iron  meteorites.  The  former  outnumber  the  latter 
twenty  to  one;  but  many  stone  meteorites  contain 
grains  of  iron.  Nickel  is  commonly  found  in  iron 
meteorites,  so  that  it  might  be  said  that  that  redoubt- 
able alloy  nickel-steel  is  of  cosmical  invention.  Some 
twenty-five  chemical  elements  have  been  found  in 
meteorites,  including  carbon  and  the  "sun-metal," 
helium.  The  presence  of  the  latter  is  certainly  high- 
ly suggestive  in  connection  with  the  question  of  the 
origin  of  meteorites.  The  iron  meteorites,  besides 
metallic  iron  and  nickel,  of  which  they  are  almost  en- 
tirely composed,  contain  hydrogen,  helium,  and  car- 
bonic oxide,  and  about  the  only  imaginable  way  in 
which  these  gases  could  have  become  absorbed  in  the 
iron  would  be  through  the  immersion  of  the  latter 
while  in  a  molten  or  vaporized  state  in  a  hot  and 



dense  atmosphere  composed  of  them,  a  condition 
which  we  know  to  exist  only  in  the  envelopes  of  the 
sun  and  the  stars. 

The  existence  of  carbon  in  the  Canyon  Diablo  iron 
meteorites  is  attended  by  a  circumstance  of  the  most 
singular  character — a  very  "fairy  tale  of  science." 
In  some  cases  the  carbon  has  become  diamond!  These 
meteoric  diamonds  are  very  small;  nevertheless,  they 
are  true  diamonds,  resembling  in  many  ways  the  little 
black  gems  produced  by  Moissan's  method  with  the 
aid  of  the  electric  furnace.  The  fact  that  they  are 
found  embedded  in  these  iron  meteorites  is  another 
argument  in  favor  of  the  hypothesis  of  the  solar  or 
stellar  origin  of  the  latter.  To  appreciate  this  it  is 
necessary  to  recall  the  way  in  which  Moissan  made  his 
diamonds.  It  was  by  a  combination  of  the  effects  of 
great  heat,  great  pressure,  and  sudden  or  rapid  super- 
ficial cooling  on  a  mass  of  iron  containing  carbon. 
When  he  finally  broke  open  his  iron  he  found  it  a 
pudding  stuffed  with  miniature  black  diamonds. 
When  a  fragment  of  the  Canyon  Diablo  meteoric  iron 
was  polished  in  Philadelphia  over  fifteen  years  ago  it 
cut  the  emery-wheel  to  pieces,  and  examination 
showed  that  the  damage  had  been  effected  by  micro- 
scopic diamonds  peppered  through  the  mass.  How 
were  those  diamonds  formed?  If  the  sun  or  Sirius 
was  the  laboratory  that  prepared  them,  we  can  get  a 
glimpse  at  the  process  of  their  formation.  There  is 
plenty  of  heat,  plenty  of  pressure,  and  an  abundance 
of  vaporized  iron  in  the  sun  and  the  stars.  When  a 
great  solar  eruption  takes  place,  masses  of  iron  which 
have  absorbed  carbon  may  be  shot  out  with  a  velocity 



whidi  forbids  their  return.  Plunged  into  the  fright- 
ful cold  of  space,  their  surfaces  are  quickly  cooled,  as 
Moissan  cooled  his  prepared  iron  by  throwing  it  into 
water,  and  thus  the  requisite  stress  is  set  up  within, 
and,  as  the  iron  solidifies,  the  included  carbon  crys- 
tallizes into  diamonds.  Whether  this  explanation  has 
a  germ  of  truth  in  it  or  not,  at  any  rate  it  is  evident 
that  iron  meteorites  were  not  created  in  the  form  in 
which  they  come  to  us;  they  must  once  have  been 
parts  of  immeasurably  more  massive  bodies  than 

The  fall  of  meteorites  offers  an  appreciable,  though 
numerically  insignificant,  peril  to  the  inhabitants  of 
the  earth.  Historical  records  show  perhaps  three  or 
four  instances  of  people  being  killed  by  these  bodies. 
But  for  the  protection  afforded  by  the  atmosphere, 
which  acts  as  a  very  effective  shield,  the  danger 
would  doubtless  be  very  much  greater.  In  the 
absence  of  an  atmosphere  not  only  would  more 
meteorites  reach  the  ground,  but  their  striking  force 
would  be  incomparably  greater,  since,  as  we  have 
seen,  the  larger  part  of  their  original  velocity  is  de- 
stroyed by  the  resistance  of  the  air.  A  meteorite 
weighing  many  tons  and  striking  the  earth  with  a 
velocity  of  twenty  or  thirty  miles  per  second,  would 
probably  cause  frightful  havoc. 

It  is  a  singular  fact  that  recent  investigations 
seem  to  have  proved  that  an  event  of  this  kind  actu- 
ally happened  in  North  America — perhaps  not  longer 
than  a  thousand  or  two  thousand  years  ago.  The 
scene  of  the  supposed  catastrophe  is  in  northern 
central  Arizona,  at  Coon  Butte,  where  there  is  a 



nearly  circular  crater  in  the  middle  of  a  circular 
elevation  or  small  mountain.  The  crater  is  some- 
what over  four  thousand  feet  in  diameter,  and  the 
surrounding  rim,  formed  of  upturned  strata  and 
ejected  rock  fragments,  rises  at  its  highest  point 
one  hundred  and  sixty  feet  above  the  plain.  The 
crater  is  about  six  hundred  feet  in  depth — that  is,  from 
the  rim  to  the  visible  floor  or  bottom  of  the  crater. 
There  is  no  evidence  that  volcanic  action  has  ever 
taken  place  in  the  immediate  neighborhood  of  Coon 
Butte.  The  rock  in  which  the  crater  has  been  made 
is  composed  of  horizontal  sandstone  and  limestone 
strata.  Between  three  hundred  and  four  hundred 
million  tons  of  rock  fragments  have  been  detached, 
and  a  large  portion  hurled  by  some  cause  out  of  the 
crater.  These  fragments  lie  concentrically  distribut- 
ed around  the  crater,  and  in  large  measure  form  the 
elevation  known  as  Coon  Butte.  The  region  has  been 
famous  for  nearly  twenty  years  on  account  of  the 
masses  of  meteoric  iron  found  scattered  about  and 
known  as  the  "Canyon  Diablo"  meteorites.  It  was 
one  of  these  masses,  which  consist  of  nickel-iron  con- 
taining a  small  quantity  of  platinum,  and  of  which 
in  all  some  ten  tons  have  been  recovered  for  sale  to 
the  various  collectors  throughout  the  world,  that  as 
before  mentioned  destroyed  the  grinding  -  tool  at 
Philadelphia  through  the  cutting  power  of  its  em- 
bedded diamonds.  These  meteoric  irons  are  scattered 
about  the  crater-hill,  in  concentric  distribution,  to  a 
maximum  distance  of  about  five  miles.  When  the 
suggestion  was  first  made  in  1896  that  a  monster 
meteorite  might  have  created  by  its  fall  this  singular 



lone  crater  in  stratified  rocks,  it  was  greeted  with  in- 
credulous smiles;  but  since  then  the  matter  has  as- 
sumed a  different  aspect.  The  Standard  Iron  Com- 
pany, formed  by  Messrs.  D.  M.  Barringer,  B.  C. 
Tilghman,  E.  J.  Bennitt,  and  S.  J.  Holsinger,  having 
become,  in  1903,  the  owner  of  this  freak  of  nature, 
sunk  shafts  and  bored  holes  to  a  great  depth  in  the 
interior  of  the  crater,  and  also  trenched  the  slopes  of 
the  mountain,  and  the  result  of  their  investigations 
has  proved  that  the  meteoric  hypothesis  of  origin  is 
correct.  (See  the  papers  published  in  the  Proceedings 
of  the  Academy  of  Natural  Sciences  of  Philadelphia, 
December,  1905,  wherein  it  is  proved  that  the  United 
States  Geological  Survey  was  wrong  in  believing  this 
crater  to  have  been  due  to  a  steam  explosion.  Since 
that  date  there  has  been  discovered  a  great  amount 
of  additional  confirmatory  proof.)  Material  of  unmis- 
takably meteoric  origin  was  found  by  means  of  the 
drills,  mixed  with  crushed  rock,  to  a  depth  of  six 
hundred  to  seven  hundred  feet  below  the  floor  of  the 
crater,  and  a  great  deal  of  it  has  been  found  admixed 
with  the  ejected  rock  fragments  on  the  outer  slopes 
of  the  mountain,  absolutely  proving  synchronism  be- 
tween the  two  events,  the  formation  of  this  great 
crater  and  the  falling  of  the  meteoric  iron  out  of  the 
sky.  The  drill  located  in  the  bottom  of  the  crater 
was  sent,  in  a  number  of  cases,  much  deeper  (over  one 
thousand  feet)  into  unaltered  horizontal  red  sand- 
stone strata,  but  no  meteoric  material  was  found 
below  this  depth  (seven  hundred  feet,  or  between 
eleven  and  twelve  hundred  feet  below  the  level  of  the 
surrounding  plain),  which  has  been  assumed  as  being 
«  207 


about  the  limit  of  penetration.  It  is  not  possible 
to  sink  a  shaft  at  present,  owing  to  the  water  which 
has  drained  into  the  crater,  and  which  forms,  with 
the  finely  pulverized  sandstone,  a  very  troublesome 
quicksand  encountered  at  about  two  hundred  feet 
below  the  visible  floor  of  the  crater.  As  soon  as  this 
water  is  removed  by  pumping  it  will  be  easy  to  explore 
the  depths  of  the  crater  by  means  of  shafts  and  drifts. 
The  rock  strata  (sandstone  and  limestone)  of  which 
the  walls  consist  present  every  appearance  of  having 
been  violently  upturned  by  a  huge  body  penetrating 
the  earth  like  a  cannon-ball.  The  general  aspect  of 
the  crater  strikingly  resembles  the  impression  made 
by  a  steel  projectile  shot  into  an  armor-plate.  Mr. 
Tilghman  has  estimated  that  a  meteorite  about  five 
hundred  feet  in  diameter  and  moving  with  a  velocity 
of  about  five  miles  per  second  would  have  made  just 
such  a  perforation  upon  striking  rocks  of  the  character 
of  those  found  at  this  place.  There  was  some  fusion 
of  the  colliding  masses,  and  the  heat  produced  some 
steam  from  the  small  amount  of  water  in  the  rocks. 
As  a  result  there  has  been  found  at  depth  a  consider- 
able amount  of  fused  quartz  (original  sandstone) ,  and 
with  it  innumerable  particles  or  sparks  of  fused 
nickel-iron  (original  meteorite).  A  projectile  of  that 
size  penetrating  eleven  to  twelve  hundred  feet  into 
the  rocky  shell  of  the  globe  must  have  produced  a 
shock  which  was  perceptible  several  hundred  miles 

The  great  velocity  ascribed  to  the  supposed  mete- 
orite at  the  moment  of  striking  could  be  accounted 
for  by  the  fact  that  it  probably  plunged  nearly 



vertically  downward,  for  it  formed  a  circular  crater 
in  the  rocky  crust  of  the  earth.  In  that  case  it 
would  have  been  less  retarded  by  the  resistance 
of  the  atmosphere  than  are  meteorites  which  enter  the 
air  at  a  lower  angle  and  shoot  ahead  hundreds  of 
miles  until  friction  has  nearly  destroyed  their  original 
motion  when  they  drop  upon  the  earth.  Some 
meteoric  masses  of  great  size,  such  as  Peary's  iron 
meteorite  found  at  Cape  York,  Greenland,  and  the 
almost  equally  large  mass  discovered  at  Bacubirito, 
Mexico,  appear  to  have  penetrated  but  slightly  on 
striking  the  earth.  This  may  be  explained  by  sup- 
posing that  they  pursued  a  long,  horizontal  course 
through  the  air  before  falling.  The  result  would  be 
that,  their  original  velocity  having  been  practically  de- 
stroyed, they  would  drop  to  the  ground  with  a  velocity 
nearly  corresponding  to  that  which  gravity  would 
impart  within  the  perpendicular  distance  of  their 
final  fall.  A  six-hundred-and-sixty-pound  meteorite, 
which  fell  at  Knyahinya,  Hungary,  striking  at  an 
angel  of  27°  from  the  vertical,  penetrated  the  ground 
to  a  depth  of  eleven  feet. 

It  has  been  remarked  that  the  Coon  Butte  meteor- 
ite may  have  fallen  not  longer  ago  than  a  few  thou- 
sand years.  This  is  based  upon  the  fact  that  the 
geological  indications  favor  the  supposition  that  the 
event  did  not  occur  more  than  five  thousand  years 
ago,  while  on  the  other  hand  the  rings  of  growth 
in  the  cedar-trees  growing  on  the  slopes  of  the  crater 
show  that  they  have  existed  there  about  seven  hun- 
dred years.  Prof.  William  H.  Pickering  has  recently 
correlated  this  with  an  ancient  chronicle  which  states 



that  at  Cairo,  Egypt,  in  the  year  1029,  "many  stars 
passed  with  a  great  noise."  He  remarks  that  Cairo 
is  about  100°,  by  great  circle,  from  Coon  Butte,  so 
that  if  the  meteorite  that  made  the  crater  was  a 
member  of  a  flock  of  similar  bodies  which  encountered 
the  earth  moving  in  parallel  lines,  some  of  them  might 
have  traversed  the  sky  tangent  to  the  earth's  surface 
at  Cairo.  That  the  spectacle  spoken  of  in  the  chron- 
icle was  caused  by  meteorites  he  deems  exceedingly 
probable  because  of  what  is  said  about ' '  a  great  noise ' ' ; 
meteorites  are  the  only  celestial  phenomena  attended 
with  perceptible  sounds.  Professor  Pickering  con- 
jectures that  this  supposed  flock  of  great  meteorites 
may  have  formed  the  nucleus  of  a  comet  which  struck 
the  earth,  and  he  finds  confirmation  of  the  idea  in  the 
fact  that  out  of  the  ten  largest  meteorites  known,  no 
less  than  seven  were  found  within  nine  hundred  miles 
of  Coon  Butte.  It  would  be  interesting  if  we  could 
trace  back  the  history  of  that  comet,  and  find  out  wrhat 
malicious  planet  caught  it  up  in  its  innocent  wan- 
derings and  hurled  it  with  so  true  an  aim  at  the  earth! 
This  remarkable  crater  is  one  of  the  most  interesting 
places  in  the  world,  for  there  is  absolutely  no  record 
of  such  a  mass,  possibly  an  iron-headed  comet,  from 
outer  space  having  come  into  collision  with  our  earth. 
The  results  of  the  future  exploration  of  the  depths  of 
the  crater  will  be  awaited  with  much  interest. 



HPHERE  are  sympathetic  moods  under  whose  in- 
1  fluence  one  gazes  with  a  certain  poignant  ten- 
derness at  the  worn  face  of  the  moon;  that  little 
''fossil  world"  (the  child  of  our  mother  earth,  too) 
bears  such  terrible  scars  of  its  brief  convulsive  life 
that  a  sense  of  pity  is  awakened  by  the  sight.  The 
moon  is  the  wonder-land  of  the  telescope.  Those 
towering  mountains,  whose  "proud  aspiring  peaks" 
cast  silhouettes  of  shadow  that  seem  drawn  with  india- 
ink ;  those  vast  plains,  enchained  with  gentle  winding 
hills  and  bordered  with  giant  ranges;  those  oval 
"oceans,"  where  one  looks  expectant  for  the  flash  of 
wind-whipped  waves;  those  enchanting  "bays"  and 
recesses  at  the  seaward  feet  of  the  Alps;  those  broad 
straits  passing  between  guardian  heights  incom- 
parably mightier  than  Gibraltar;  those  locket-like 
valleys  as  secluded  among  their  mountains  as  the 
Vale  of  Cashmere;  those  colossal  craters  that  make 
us  smile  at  the  pretensions  of  Vesuvius,  Etna,  and 
Cotopaxi;  those  strange  white  ways  which  pass  with 
the  unconcern  of  Roman  roads  across  mountain,  gorge, 
and  valley — all  these  give  the  beholder  an  irresistible 
impression  that  it  is  truly  a  world  into  which  he  is 



looking,  a  world  akin  to  ours,  and  yet  no  more  like 
our  world  than  Pompeii  is  like  Naples.  Its  air,  its 
waters,  its  clouds,  its  life  are  gone,  and  only  a  skeleton 
remains — a  mute  but  eloquent  witness  to  a  cosmical 
tragedy  without  parallel  in  the  range  of  human 

One  cannot  but  regret  that  the  moon,  if  it  ever  was 
the  seat  of  intelligent  life,  has  not  remained  so  until 
our  time.  Think  what  the  consequences  would  have 
been  if  this  other  world  at  our  very  door  had  been 
found  to  be  both  habitable  and  inhabited!  We  talk 
rather  airily  of  communicating  with  Mars  by  signals; 
but  Mars  never  approaches  nearer  than  35,000,000 
miles,  while  the  moon  when  nearest  is  only  a  little  more 
than  2 20 ,000  miles  away.  Given  an  effective  magnify- 
ing power  of  five  thousand  diameters,  which  will  per- 
haps be  possible  at  the  mountain  observatories  as 
telescopes  improve,  and  we  should  be  able  to  bring 
the  moon  within  an  apparent  distance  of  about  forty 
miles,  while  the  corresponding  distance  for  Mars  would 
be  more  than  seven  thousand  miles.  But  even  with 
existing  telescopic  powers  we  can  see  details  on  the 
moon  no  larger  than  some  artificial  constructions  on 
the  earth.  St.  Peter's  at  Rome,  with  the  Vatican 
palace  and  the  great  piazza,  if  existing  on  the  moon, 
would  unquestionably  be  recognizable  as  something 
else  than  a  freak  of  nature.  Large  cities,  with  their 
radiating  lines  of  communication,  would  at  once  be- 
tray their  real  character.  Cultivated  tracts,  and  the 
changes  produced  by  the  interference  of  intelligent 
beings,  would  be  clearly  recognizable.  The  electric 
illumination  of  a  large  town  at  night  would  probably 



be  markedly  visible.  Gleams  of  reflected  sunlight 
would  come  to  us  from  the  surfaces  of  the  lakes  and 
oceans,  and  a  huge  "liner"  traversing  a  lunar  sea 
could  probably  be  followed  by  its  trail  of  smoke.  As 
to  communications  by  "wireless"  signals,  which  cer- 
tain enthusiasts  have  thought  of  in  connection  with 
Mars,  in  the  case  of  the  moon  they  should  be  a  rela- 
tively simple  matter,  and  the  feat  might  actually  be 
accomplished.  Think  what  a  literature  would  grow 
up  about  the  moon  if  it  were  a  living  world !  Its  very 
differences  from  the  earth  would  only  accentuate  its 
interest  for  us.  Night  and  day  on  the  moon  are  each 
two  weeks  in  length;  how  interesting  it  would  be  to 
watch  the  manner  in  which  the  lunarians  dealt  with 
such  a  situation  as  that.  Lunar  and  terrestrial  history 
would  keep  step  with  each  other,  and  we  should  record 
them  both.  Truly  one  might  well  wish  to  have  a 
neighbor  world  to  study;  one  would  feel  so  much  the 
less  alone  in  space. 

It  is  not  impossible  that  the  moon  did  at  one  time 
have  inhabitants  of  some  kind.  But,  if  so,  they  van- 
ished with  the  disappearance  of  its  atmosphere  and 
seas,  or  with  the  advent  of  its  cataclysmic  age.  At  the 
best,  its  career  as  a  living  world  must  have  been  brief. 
If  the  water  and  air  were  gradually  absorbed,  as  some 
have  conjectured,  by  its  cooling  interior  rocks,  its  sur- 
face might,  nevertheless,  have  retained  them  for  long 
ages;  but  if,  as  others  think,  their  disappearance  was 
due  to  the  escape  of  their  gaseous  molecules  in  con- 
sequence of  the  inability  of  the  relatively, small  lunar 
gravitation  to  retain  them,  then  the  final  catastrophe 
must  have  been  as  swift  as  it  was  inevitable.  Ac- 



cepting  Darwin's  hypothesis,  that  the  moon  was 
separated  from  the  earth  by  tidal  action  while  both 
were  yet  plastic  or  nebulous,  we  may  reasonably  con- 
clude that  it  began  its  career  with  a  good  supply  of 
both  water  and  air,  but  did  not  possess  sufficient 
mass  to  hold  them  permanently.  Yet  it  may  have 
retained  them  long  enough  for  life  to  develop  in 
many  forms  upon  its  surface;  in  fact,  there  are  so 
many  indications  that  air  and  water  have  not  always 
been  lacking  to  the  lunar  world  that  we  are  driven 
to  invent  theories  to  explain  both  their  former  presence 
and  their  present  absence. 

But  whatever  the  former  condition  of  the  moon 
may  have  been,  its  existing  appearance  gives  it  a 
resistless  fascination,  and  it  bears  so  clearly  the  story 
of  a  vast  catastrophe  sculptured  on  its  rocky  face  that 
the  thoughtful  observer  cannot  look  upon  it  without 
a  feeling  of  awe.  The  gigantic  character  of  the  lunar 
features  impresses  the  beholder  not  less  than  the  uni- 
versality of  the  play  of  destructive  forces  which  they 
attest.  Let  us  make  a  few  comparisons.  Take  the 
lunar  crater  called  "Tycho,"  which  is  a  typical  ex- 
ample of  its  kind.  In  the  telescope  Tycho  appears  as  a 
perfect  ring  surrounding  a  circular  depression,  in  the 
centre  of  which  rises  a  group  of  mountains.  Its 
superficial  resemblance  to  some  terrestrial  volcanic 
craters  is  very  striking.  Vesuvius,  seen  from  a  point 
vertically  above,  would  no  doubt  look  something  like 
that  (the  resemblance  would  have  been  greater  when 
the  Monte  del  Cavallo  formed  a  more  complete  circuit 
about  the  crater  cone) .  But  compare  the  dimensions. 
The  remains  of  the  outer  crater  ring  of  Vesuvius  are 





perhaps  half  a  mile  in  diameter,  while  the  active  crater 
itself  is  only  two  or  three  hundred  feet  across  at  the 
most;  Tycho  has  a  diameter  of  fifty- four  miles!  The 
group  of  relatively  insignificant  peaks  in  the  centre  of 
the  crater  floor  of  Tycho  is  far  more  massive  than  the 
entire  mountain  that  we  call  Vesuvius.  The  largest 
known  volcanic  crater  on  the  earth,  Aso  San,  in  Japan, 
has  a  diameter  of  seven  miles;  it  would  take  sixty 
craters  like  Aso  San  to  equal  Tycho  in  area!  And 
Tycho,  though  one  of  the  most  perfect,  is  by  no  means 
the  largest  crater  on  the  moon.  Another,  called 
"Theophilus,"  has  a  diameter  of  sixty- four  miles,  and 
is  eighteen  thousand  feet  deep.  There  are  hundreds 
from  ten  to  forty  miles  in  diameter,  and  thousands 
from  one  to  ten  miles.  They  are  so  numerous  in 
many  places  that  they  break  into  one  another,  like  the 
cells  of  a  crushed  honeycomb. 

The  lunar  craters  differ  from  those  of  the  earth  more 
fundamentally  than  in  the  matter  of  mere  size ;  they 
are  not  situated  on  the  tops  of  mountains.  If  they  were, 
and  if  all  the  proportions  were  the  same,  a  crater  like 
Tycho  might  crown  a  conical  peak  fifty  or  one  hundred 
miles  high!  Instead  of  being  cavities  in  the  summits 
of  mountains,  the  lunar  craters  are  rather  gigantic  sink- 
holes whose  bottoms  in  many  cases  lie  two  or  three 
miles  below  the  general  surface  of  the  lunar  world. 
Around  their  rims  the  rocks  are  piled  up  to  a  height 
of  from  a  few  hundred  to  two  or  three  thousand  feet, 
with  a  comparatively  gentle  inclination,  but  on  the 
inner  side  they  fall  away  in  gigantic  broken  precipices 
which  make  the  dizzy  cliffs  of  the  Matterhorn  seem 
but  "lover's  leaps."  Down  they  drop,  ridge  below 



ridge  crag  under  crag,  tottering  wall  beneath  wall,  un- 
til, in  a  crater  named  "  Newton,"  near  the  south  lunar 
pole,  they  attain  a  depth  where  the  rays  of  the  sun 
never  reach.  Nothing  more  frightful  than  the  spec- 
tacle which  many  of  these  terrible  chasms  present  can 
be  pictured  by  the  imagination.  As  the  lazy  lunar 
day  slowly  advances,  the  sunshine,  unmitigated  by 
clouds  or  atmospheric  veil  of  any  kind,  creeps  across 
their  rims  and  begins  to  descend  the  opposite  walls. 
Presently  it  strikes  the  ragged  crest  of  a  ridge  which 
had  lain  hidden  in  such  darkness  as  we  never  know 
on  the  earth,  and  runs  along  it  like  a  line  of  kindling 
fire.  Rocky  pinnacles  and  needles  shoot  up  into  the 
sunlight  out  of  the  black  depths.  Down  sinks  the 
line  of  light,  mile  after  mile,  and  continually  new 
precipices  and  cliffs  are  brought  into  view,  until  at 
last  the  vast  floor  is  attained  and  begins  to  be  illumi- 
nated. In  the  mean  while  the  sun's  rays,  darting 
across  the  gulf,  have  touched  the  summits  of  the 
central  peaks,  twenty  or  thirty  miles  from  the  crater's 
inmost  edge,  and  they  immediately  kindle  and  blaze 
like  huge  stars  amid  the  darkness.  So  profound  are 
some  of  these  awful  craters  that  days  pass  before  the 
sun  has  risen  high  enough  above  them  to  chase  the 
last  shadows  from  their  depths. 

Although  several  long  ranges  of  mountains  resem- 
bling those  of  the  earth  exist  on  the  moon,  the  great 
majority  of  its  elevations  assume  the  crateriform  as- 
pect. Sometimes,  instead  of  a  crater,  we  find  an 
immense  mountain  ring  whose  form  and  aspect  hard- 
ly suggest  volcanic  action.  But  everywhere  the  true 
craters  are  in  evidence,  even  on  the  sea-beds,  al- 



though  they  attain  their  greatest  number  and  size 
on  those  parts  of  the  moon — covering  sixty  per  cent, 
of  its  visible  surface — which  are  distinctly  mountain- 
ous in  character  and  which  constitute  its  most  brill- 
iant portions.  Broadly  speaking,  the  southwestern 
half  of  the  moon  is  the  most  mountainous  and  broken, 
and  the  northeastern  half  the  least  so.  Right  down 
through  the  centre,  from  pole  to  pole,  runs  a  wonder- 
ful line  of  craters  and  crateriform  valleys  of  a  magni- 
tude stupendous  even  for  the  moon.  Another  similar 
line  follows  the  western  edge.  Three  or  four  "seas" 
are  thrust  between  these  mountainous  belts.  By  the 
effects  of  "libration"  parts  of  the  opposite  hemi- 
sphere of  the  moon  which  is  turned  away  from  the 
earth  are  from  time  to  time  brought  into  view,  and 
their  aspect  indicates  that  that  hemisphere  resembles 
in  its  surface  features  the  one  which  faces  the  earth. 
There  are  many  things  about  the  craters  which  seem 
to  give  some  warrant  for  the  hypothesis  which  has 
been  particularly  urged  by  Mr.  W.  K.  Gilbert,  that 
they  were  formed  by  the  impact  of  meteors;  but 
there  are  also  many  things  which  militate  against 
that  idea,  and,  upon  the  whole,  the  volcanic  theory 
of  their  origin  is  to  be  preferred. 

The  enormous  size  of  the  lunar  volcanoes  is  not  so 
difficult  to  account  for  when  we  remember  how  slight 
is  the  force  of  lunar  gravity  as  compared  with  that  of 
the  earth.  With  equal  size  and  density,  bodies  on 
the  moon  weigh  only  one-sixth  as  much  as  on  the 
earth.  Impelled  by  the  same  force,  a  projectile  that 
would  go  ten  miles  on  the  earth  would  go  sixty  miles 
on  the  moon.  A  lunar  giant  thirty-five  feet  tall 



would  weigh  no  more  than  an  ordinary  son  of  Adam 
weighs  on  his  greater  planet.  To  shoot  a  body  from 
the  earth  so  that  it  would  not  drop  back  again,  we 
should  have  to  start  it  with  a  velocity  of  seven  miles 
per  second;  a  mile  and  a  half  per  second  would  serve 
on  the  moon.  It  is  by  no  means  difficult  to  believe, 
then,  that  a  lunar  volcano  might  form  a  crater  ring 
eight  or  ten  times  broader  than  the  greatest  to  be 
found  on  the  earth,  especially  when  we  reflect  that 
in  addition  to  the  relatively  slight  force  of  gravity, 
the  materials  of  the  lunar  crust  are  probably  lighter 
than  those  of  our  terrestrial  rocks. 

For  similar  reasons  it  seems  not  impossible  that 
the  theory  mentioned  in  a  former  chapter — that 
some  of  the  meteorites  that  have  fallen  upon  the 
earth  originated  from  the  lunar  volcanoes — is  well 
founded.  This  would  apply  especially  to  the  stony 
meteorites,  for  it  is  hardly  to  be  supposed  that  the 
moon,  at  least  in  its  superficial  parts,  contains  much 
iron.  It  is  surely  a  scene  most  strange  that  is  thus 
presented  to  the  mind's  eye — that  little  attendant 
of  the  earth's  (the  moon  has  only  one-fiftieth  of  the 
volume,  and  only  one-eightieth  of  the  mass  of  the 
earth)  firing  great  stones  back  at  its  parent  planet! 
And  what  can  have  been  the  cause  of  this  furious 
outbreak  of  volcanic  forces  on  the  moon?  Evidently 
it  was  but  a  passing  stage  in  its  history;  it  had  en- 
joyed more  quiet  times  before.  As  it  cooled  down 
from  the  plastic  state  in  which  it  parted  from  the 
earth,  it  became  incrusted  after  the  normal  manner 
of  a  planet,  and  then  oceans  were  formed,  its  atmos- 
phere being  sufficiently  dense  to  prevent  the  water 




from  evaporating  and  the  would-be  oceans  from  dis- 
appearing continually  in  mist.  This,  if  any,  must 
have  been  the  period  of  life  in  the  lunar  world.  As 
we  look  upon  the  vestiges  of  that  ancient  world  buried 
in  the  wreck  that  now  covers  so  much  of  its  surface, 
it  is  difficult  to  restrain  the  imagination  from  pictur- 
ing the  scenes  which  were  once  presented  there ;  and, 
in  such  a  case,  should  the  imagination  be  fettered? 
We  give  it  free  rein  in  terrestrial  life,  and  it  rewards 
us  with  some  of  our  greatest  intellectual  pleasures. 
The  wonderful  landscapes  of  the  moon  offer  it  an 
ideal  field  with  just  enough  half-hidden  suggestions 
of  facts  to  stimulate  its  powers. 

The  great  plains  of  the  Mare  Imbrium  and  the  Mare 
Serenitatis  (the  "Sea  of  Showers"  and  the  "Sea  of 
Serenity"),  bordered  in  part  by  lofty  mountain 
ranges  precisely  like  terrestrial  mountains,  scalloped 
along  their  shores  with  beautiful  bays  curving  back 
into  the  adjoining  highlands,  and  united  by  a  great 
strait  passing  between  the  nearly  abutting  ends  of 
the  "Lunar  Apennines"  and  the  "Lunar  Caucasus," 
offer  the  elements  of  a  scene  of  world  beauty  such  as 
it  would  be  difficult  to  match  upon  our  planet.  Look 
at  the  finely  modulated  bottom  of  the  ancient  sea  in 
Mr.  Ritchey's  exquisite  photograph  of  the  western 
part  of  the  Mare  Serenitatis,  where  one  seems  to  see 
the  play  of  the  watery  currents  heaping  the  ocean 
sands  in  waving  lines,  making  shallows,  bars,  and 
deeps  for  the  mariner  to  avoid  or  seek,  and  affording 
a  playground  for  the  creatures  of  the  main.  What 
geologist  would  not  wish  to  try  his  hammer  on  those 
rocks  with  their  stony  pages  of  fossilized  history? 



There  is  in  us  an  instinct  which  forbids  us  to  think 
that  there  was  never  any  life  there.  If  we  could 
visit  the  moon,  there  is  not  among  us  a  person  so 
prosaic  and  unimaginative  that  he  would  not,  the 
very  first  thing,  begin  to  search  for  traces  of  its  in- 
habitants. We  would  look  for  them  in  the  deposits 
on  the  sea  bottoms;  we  would  examine  the  shores 
wherever  the  configuration  seemed  favorable  for  har- 
bors and  the  sites  of  maritime  cities — forgetting  that 
it  may  be  a  little  ridiculous  to  ascribe  to  the  ancient 
lunarians  the  same  ideas  that  have  governed  the  de- 
velopment of  our  race;  we  would  search  through  the 
valleys  and  along  the  seeming  courses  of  vanished 
streams;  we  would  explore  the  mountains,  not  the 
terrible  craters,  but  the  pinnacled  chains  that  recall 
our  own  Alps  and  Rockies ;  seeking  everywhere  some 
vestige  of  the  transforming  presence  of  intelligent 
life.  Perhaps  we  should  find  such  traces,  and  per- 
haps, with  all  our  searching,  we  should  find  nothing 
to  suggest  that  life  had  ever  existed  amid  that  uni- 
versal ruin. 

Look  again  at  the  border  of  the  "Sea  of  Serenity" 
— what  a  name  for  such  a  scene! — and  observe  how 
it  has  been  rent  with  almost  inconceivable  violence, 
the  wall  of  the  colossal  crater  Posidonius  dropping 
vertically  upon  the  ancient  shore  and  obliterating  it, 
while  its  giant  neighbor,  Le  Monnier,  opens  a  yawn- 
ing mouth  as  if  to  swallow  the  sea  itself.  A  scene 
like  this  makes  one  question  whether,  after  all,  those 
may  not  be  right  who  have  imagined  that  the  so-called 
sea  bottoms  are  really  vast  plains  of  frozen  lava 
which  gushed  up  in  floods  so  extensive  that  even 




the  mighty  volcanoes  were  half  drowned  in  the  fiery 
sea.  This  suggestion  becomes  even  stronger  when 
we  turn  to  another  of  the  photographs  of  Mr.  Ritchey 's 
wonderful  series,  showing  a  part  of  the  Mare  Tran- 
quilitatis  ("Sea  of  Tranquility " !) .  Notice  how  near 
the  centre  of  the  picture  the  outline  of  a  huge  ring 
with  radiating  ridges  shows  through  the  sea  bottom; 
a  fossil  volcano  submerged  in  a  petrified  ocean! 
This  is  by  no  means  the  only  instance  in  which  a 
buried  world  shows  itself  under  the  great  lunar  plains. 
Yet,  as  the  newer  craters  in  the  sea  itself  prove,  the 
volcanic  activity  survived  this  other  catastrophe,  or 
broke  out  again  subsequently,  bringing  more  ruin  to 
pile  upon  ruin. 

Yet  notwithstanding  the  evidence  which  we  have 
just  been  considering  in  support  of  the  hypothesis 
that  the  "seas"  are  lava  floods,  Messrs.  Loewy  and 
Puiseux,  the  selenographers  of  the  Paris  Observatory, 
are  convinced  that  these  great  plains  bear  character- 
istic marks  of  the  former  presence  of  immense  bodies 
of  water.  In  that  case  we  should  be  forced  to  con- 
clude that  the  later  oceans  of  the  moon  lay  upon  vast 
sheets  of  solidified  lava ;  and  thus  the  catastrophe  of 
the  lunar  world  assumes  a  double  aspect,  the  earliest 
oceans  being  swallowed  up  in  molten  floods  issuing 
from  the  interior,  while  the  lands  were  reduced  to 
chaos  by  a  universal  eruption  of  tremendous  vol- 
canoes; and  then  a  period  of  comparative  quiet  fol- 
lowed, during  which  new  seas  were  formed,  and  new 
life  perhaps  began  to  flourish  in  the  lunar  world,  only 
to  end  in  another  cataclysm,  which  finally  put  a  term 
to  the  existence  of  the  moon  as  a  life-supporting  world. 



Suppose  we  examine  two  more  of  Mr.  Ritchey's 
illuminating  photographs,  and,  first,  the  one  showing 
the  crater  Theophilus  and  its  surroundings.  We  have 
spoken  of  Theophilus  before,  citing  the  facts  that  it  is 
sixty-four  miles  in  diameter  and  eighteen  thousand  feet 
deep.  It  will  be  noticed  that  it  has  two  brother 
giants — Cyrillus  the  nearer,  and  Catharina  the  more 
distant;  but  Theophilus  is  plainly  the  youngest  of 
the  trio.  Centuries,  and  perhaps  thousands  of  years, 
must  have  elapsed  between  the  periods  of  their  up- 
heaval, for  the  two  older  craters  are  partly  filled 
with  debris,  while  it  is  manifest  at  a  glance  that 
when  the  southeastern  wall  of  Theophilus  was  formed, 
it  broke  away  and  destroyed  a  part  of  the  more 
ancient  ring  of  Cyrillus.  There  is  no  more  tremendous 
scene  on  the  moon  than  this ;  viewed  with  a  powerful 
telescope,  it  is  absolutely  appalling. 

The  next  photograph  shows,  if  possible,  a  still 
wilder  region.  It  is  the  part  of  the  moon  lying  be- 
tween Tycho  and  the  south  pole.  Tycho  is  seen  in 
the  lower  left-hand  part  of  the  picture.  To  the  right, 
at  the  edge  of  the  illuminated  portion  of  the  moon, 
are  the  crater-rings,  Longomontanus  and  Wilhelm  I., 
the  former  being  the  larger.  Between  them  are  to 
be  seen  the  ruins  of  two  or  three  more  ancient  craters 
which,  together  with  portions  of  the  walls  of  Wilhelm 
I.  and  Longomontanus,  have  been  honeycombed 
with  smaller  craters.  The  vast  crateriform  depression 
above  the  centre  of  the  picture  is  Clavius,  an  un- 
rivalled wonder  of  lunar  scenery,  a  hundred  and 
forty-two  miles  in  its  greatest  length,  while  its  whole 
immense  floor  has  sunk  two  miles  below  the  general 




surface  of  the  moon  outside  the  ring.  The  monstrous 
shadow-filled  cavity  above  Clavius  toward  the  right 
is  Blancanus,  whose  aspect  here  gives  a  good  idea  of 
the  appearance  of  these  chasms  when  only  their  rims 
are  in  the  sunlight.  But  observe  the  indescribable 
savagery  of  the  entire  scene.  It  looks  as  though 
the  spirit  of  destruction  had  gone  mad  in  this  spot. 
The  mighty  craters  have  broken  forth  one  after  an- 
other, each  rending  its  predecessor;  and  when  their 
work  was  finished,  a  minor  but  yet  tremendous  out- 
break occurred,  and  the  face  of  the  moon  was  gored 
and  punctured  with  thousands  of  smaller  craters. 
These  relatively  small  craters  (small,  however,  only  in 
a  lunar  sense,  for  many  of  them  would  appear  gigantic 
on  the  earth)  recall  once  more  the  theory  of  meteoric 
impact.  It  does  not  seem  impossible  that  some  of 
them  may  have  been  formed  by  such  an  agency. 

One  would  not  wish  for  our  planet  such  a  fate  as 
that  which  has  overtaken  the  moon,  but  we  cannot 
be  absolutely  sure  that  something  of  the  kind  may 
not  be  in  store  for  it.  We  really  know  nothing  of 
the  ultimate  causes  of  volcanic  activity,  and  some 
have  suggested  that  the  internal  energies  of  the  earth 
may  be  accumulating  instead  of  dying  out,  and  may 
never  yet  have  exhibited  their  utmost  destructive 
power.  Perhaps  the  best  assurance  that  we  can  find 
that  the  earth  will  escape  the  catastrophe  that  has 
overtaken  its  satellite  is  to  be  found  in  the  relatively 
great  force  of  its  gravitation.  The  moon  has  been 
the  victim  of  its  weakness;  given  equal  forces,  and  the 
earth  would  be  the  better  able  to  withstand  them. 
It  is  significant,  in  connection  with  these  considera- 



tions,  that  the  little  planet  Mercury,  which  seems 
also  to  have  parted  with  its  air  and  water,  shows  to 
the  telescope  some  indications  that  it  is  pitted  with 
craters  resembling  those  that  have  torn  to  pieces  the 
face  of  the  moon. 

Upon  the  whole,  after  studying  the  dreadful  lunar 
landscapes,  one  cannot  feel  a  very  enthusiastic  sym- 
pathy with  those  who  are  seeking  indications  of  the 
continued  existence  of  some  kind  of  life  on  the  moon; 
such  a  world  is  better  without  inhabitants.  It  has 
met  its  fate;  let  it  go!  Fortunately,  it  is  not  so  near 
that  it  cannot  hide  its  scars  and  appear  beautiful — 
except  when  curiosity  impels  us  to  look  with  the 
penetrating  eyes  of  the  astronomer. 




I  ET  any  thoughtful  person  who  is  acquainted  with 
L/the  general  facts  of  astronomy  look  up  at  the 
heavens  some  night  when  they  appear  in  their  great- 
est splendor,  and  ask  himself  what  is  the  strong- 
est impression  that  they  make  upon  his  mind.  He 
may  not  find  it  easy  to  frame  an  answer,  but  when  he 
has  succeeded  it  will  probably  be  to  the  effect  that 
the  stars  give  him  an  impression  of  the  universality 
of  intelligence;  they  make  him  feel,  as  the  sun  and 
the  moon  cannot  do,  that  his  world  is  not  alone ;  that 
all  this  was  not  made  simply  to  form  a  gorgeous 
canopy  over  the  tents  of  men.  If  he  is  of  a  devout 
turn  of  mind,  he  thinks,  as  he  gazes  into  those  fathom- 
less deeps  and  among  those  bewildering  hosts,  of  the 
infinite  multitude  of  created  beings  that  the  Al- 
mighty has  taken  under  his  care.  The  narrow  ideas 
of  the  old  geocentric  theology,  which  made  the  earth 
God's  especial  footstool,  and  man  his  only  rational 
creature,  fall  away  from  him  like  a  veil  that  had 
obscured  his  vision;  they  are  impossible  in  the  pres- 
ence of  what  he  sees  above.  Thus  the  natural  ten- 
dency, in  the  light  of  modern  progress,  is  to  regard 
the  universe  as  everywhere  filled  with  life. 



But  science,  which  is  responsible  for  this  broaden- 
ing of  men's  thoughts  concerning  the  universality  of 
life,  itself  proceeds  to  set  limits.  Of  spiritual  exist- 
ences it  pretends  to  know  nothing,  but  as  to  physical 
beings,  it  declares  that  it  can  only  entertain  the  sup- 
position of  their  existence  where  it  finds  evidence  of 
an  environment  suited  to  their  needs,  and  such  en- 
vironment may  not  everywhere  exist.  Science, 
though  repelled  by  the  antiquated  theological  con- 
ception of  the  supreme  isolation  of  man  among  created 
beings,  regards  with  complacency  the  probability 
that  there  are  regions  in  the  universe  where  no  organic 
life  exists,  stars  which  shine  upon  no  inhabited 
worlds,  and  planets  which  nourish  no  animate  creat- 
ures. The  astronomical  view  of  the  universe  is  that 
it  consists  of  matter  in  every  stage  of  evolution: 
some  nebulous  and  chaotic;  some  just  condensing 
into  stars  (suns)  of  every  magnitude  and  order;  some 
shaped  into  finished  solar  bodies  surrounded  by  de- 
pendent planets;  some  forming  stars  that  perhaps 
have  no  planets,  and  will  have  none ;  some  constitut- 
ing suns  that  are  already  aging,  and  will  soon  lose 
their  radiant  energy  and  disappear;  and  some  ag- 
gregated into  masses  that  long  ago  became  inert, 
cold,  and  rayless,  and  that  can  only  be  revivified  by 
means  about  which  we  can  form  conjectures,  but  of 
which  we  actually  know  nothing. 

As  with  the  stars,  so  with  the  planets,  which  are 
the  satellites  of  stars.  All  investigations  unite  to 
tell  us  that  the  planets  are  not  all  in  the  same  state 
of  development.  As  some  are  large  and  some  small, 
so  some  are,  in  an  evolutionary  sense,  young,  and 



some  old.  As  they  depend  upon  the  suns  around 
which  they  revolve  for  their  light,  heat,  and  other 
forms  of  radiant  energy,  so  their  condition  varies 
with  their  distance  from  those  suns.  Many  may 
never  arrive  at  a  state  suitable  for  the  maintenance 
of  life  upon  their  surfaces;  some  which  are  not  at 
present  in  such  a  state  may  attain  it  later;  and  the 
forms  of  life  themselves  may  vary  with  the  peculiar 
environment  that  different  planets  afford.  Thus  we 
see  that  we  are  not  scientifically  justified  in  affirming 
that  life  is  ubiquitous,  although  we  are  thus  justified 
in  saying  that  it  must  be,  in  a  general  sense,  universal. 
We  might  liken  the  universe  to  a  garden  known  to 
contain  every  variety  of  plant.  If  on  entering  it  we 
see  no  flowers,  we  examine  the  species  before  us  and 
find  that  they  are  not  of  those  which  bloom  at  this 
particular  season,  or  perhaps  they  are  such  as  never 
bear  flowers.  Yet  we  feel  no  doubt  that  we  shall  find 
flowers  somewhere  in  the  garden,  because  there  are 
species  which  bloom  at  this  season,  and  the  garden 
contains  all  varieties. 

While  it  is  tacitly  assumed  that  there  are  planets 
revolving  around  other  stars  than  the  sun,  it  would 
be  impossible  for  us  to  see  them  with  any  telescope 
yet  invented,  and  no  instrument  now  in  the 
posession  of  astronomers  could  assure  us  of  their 
existence;  so  the  only  planetary  system  of  which 
we  have  visual  knowledge  is  our  own.  Excluding 
the  asteroids,  which  could  not  from  any  point  of 
view  be  considered  as  habitable,  we  have  in  the  solar 
system  eight  planets  of  various  sizes  and  situated  at 
various  distances  from  the  sun.  Of  these  eight  we 



know  that  one,  the  earth,  is  inhabited.  The  ques- 
tion, then,  arises:  Are  there  any  of  the  others  which 
are  inhabited  or  habitable  ?  Since  it  is  our  intention 
to  discuss  the  habitability  of  only  one  of  the  seven 
to  which  the  question  applies,  the  rest  may  be  dis- 
missed in  a  few  words.  The  smallest  of  them,  and 
the  nearest  to  the  sun,  is  Mercury,  which  is  regarded 
as  uninhabitable  because  it  has  no  perceptible  supply 
of  water  and  air,  and  because,  owing  to  the  extraor- 
dinary eccentricity  of  its  orbit,  it  is  subjected  to 
excessive  and  very  rapid  alterations  in  the  amount 
of  solar  heat  and  light  poured  upon  its  surface,  such 
alterations  being  inconsistent  with  the  supposition 
that  it  can  support  living  beings.  Even  its  average 
temperature  is  more  than  six  and  a  half  times  that 
prevailing  on  the  earth!  Another  circumstance 
which  militates  against  its  habitability  is  that,  ac- 
cording to  the  results  of  the  best  telescopic  studies, 
it  always  keeps  the  same  face  toward  the  sun,  so  that 
one  half  of  the  planet  is  perpetually  exposed  to  the 
fierce  solar  rays,  and  the  other  half  faces  the  un- 
mitigated cold  of  open  space.  Venus,  the  next  in 
distance  from  the  sun,  is  almost  the  exact  twin  of 
the  earth  in  size,  and  many  arguments  may  be  urged 
in  favor  of  its  habitability,  although  it  is  suspected 
of  possessing  the  same  peculiarity  as  Mercury,  in 
always  keeping  the  same  side  sunward.  Unfortu- 
nately its  atmosphere  appears  to  be  so  dense  that 
no  permanent  markings  on  its  surface  are  certainly 
visible,  and  the  question  of  its  actual  condition  must, 
for  the  present,  be  left  in  abeyance.  Mars,  the  first 
planet  more  distant  from  the  sun  than  the  earth,  is 


the  special  subject  of  this  chapter,  and  will  be  de- 
scribed and  discussed  a  few  lines  further  on.  Jupiter, 
Saturn,  Uranus,  and  Neptune,  the  four  giant  planets, 
all  more  distant  than  Mars,  and  each  more  distant 
than  the  other  in  the  order  named,  are  all  regarded 
as  uninhabitable  because  none  of  them  appears  to 
possess  any  degree  of  solidity.  They  may  have  solid 
or  liquid  nuclei,  but  exteriorly  they  seem  to  be  mere 
balls  of  cloud.  Of  course,  one  can  imagine  what  he 
pleases  about  the  existence  of  creatures  suited  to  the 
physical  constitution  of  such  planets  as  these,  but 
they  must  be  excluded  from  the  category  of  habitable 
worlds  in  the  ordinary  sense  of  the  term.  We  go 
back,  then,  to  Mars. 

It  will  be  best  to  begin  with  a  description  of  the 
planet.  Mars  is  4230  miles  in  diameter;  its  surface 
is  not  much  more  than  one-quarter  as  extensive  as 
that  of  the  earth  (.285).  Its  mean  distance  from  the 
sun  is  141,500,000  miles,  48,500,000  miles  greater  than 
that  of  the  earth.  Since  radiant  energy  varies  in- 
versely as  the  square  of  distance,  Mars  receives  less 
than  half  as  much  solar  light  and  heat  as  the  earth 
gets.  Mars'  year  (period  of  revolution  round  the 
sun)  is  687  days.  Its  mean  density  is  71  per  cent, 
of  the  earth's,  and  the  force  of  gravity  on  its  surface 
is  38  per  cent,  of  that  on  the  surface  of  the  earth; 
i.e.,  a  body  weighing  one  hundred  pounds  on  the 
earth  would,  if  transported  to  Mars,  weigh  but  thirty- 
eight  pounds.  The  inclination  of  its  equator  to  the 
plane  of  its  orbit  differs  very  little  from  that  of  the 
earth's  equator,  and  its  axial  rotation  occupies  24 
hours  37  minutes;  so  that  the  length  of  day  and 



night,  and  the  extent  of  the  seasonal  changes  on 
Mars,  are  almost  precisely  the  same  as  on  the  earth. 
But  owing  to  the  greater  length  of  its  year,  the  sea- 
sons of  Mars,  while  occurring  in  the  same  order,  are 
almost  twice  as  long  as  ours.  The  surface  of  the 
planet  is  manifestly  solid,  like  that  of  our  globe,  and 
the  telescope  reveals  many  permanent  markings  on 
it,  recalling  the  appearance  of  a  globe  on  which  geo- 
graphical features  have  been  represented  in  reddish 
and  dusky  tints.  Around  the  poles  are  plainly  to 
be  seen  rounded  white  areas,  which  vary  in  extent 
with  the  Martian  seasons,  nearly  vanishing  in  sum- 
mer and  extending  widely  in  winter.  The  most 
recent  spectroscopic  determinations  indicate  that 
Mars  has  an  atmosphere  perhaps  as  dense  as  that  to 
be  found  on  our  loftiest  mountain  peaks,  and  there 
is  a  perceptible  amount  of  watery  vapor  in  this 
atmosphere.  The  surface  of  the  planet  appears  to 
be  remarkably  level,  and  it  has  no  mountain  ranges. 
No  evidences  of  volcanic  action  have  been  discovered 
on  Mars.  The  dusky  and  reddish  areas  were  re- 
garded by  the  early  observers  as  respectively  seas 
and  lands,  but  at  present  it  is  not  believed  that  there 
are  any  bodies  of  water  on  the  planet.  There  has 
never  been  much  doubt  expressed  that  the  white 
areas  about  the  poles  represent  snow. 

It  will  be  seen  from  this  brief  description  that  many 
remarkable  resemblances  exist  between  Mars  and  the 
earth,  and  there  is  nothing  wonderful  in  the  fact  that 
the  question  of  the  habitability  of  the  former  has  be- 
come one  of  extreme  and  wide-spread  interest,  giving 
rise  to  the  most  diverse  views,  to  many  extraordinary 



speculations,  and  sometimes  to  regrettably  heated 
controversy.  The  first  champion  of  the  habitability 
of  Mars  was  Sir  William  Herschel,  although  even 
before  his  time  the  idea  had  been  suggested.  He 
was  convinced  by  the  revelations  of  his  telescopes, 
continually  increasing  in  power,  that  Mars  was  more 
like  the  earth  than  any  other  planet.  He  could  not 
resist  the  testimony  of  the  polar  snows,  whose  sug- 
gestive conduct  was  in  such  striking  accord  with  what 
occurs  upon  the  earth.  Gradually,  as  telescopes  im- 
proved and  observers  increased  in  number,  the  prin- 
cipal features  of  the  planet  were  disclosed  and  charted, 
and  "areography,"  as  the  geography  of  Mars  was 
called,  took  its  place  among  the  recognized  branches 
of  astronomical  study.  But  it  was  not  before  1877 
that  a  fundamentally  new  discovery  in  areography 
gave  a  truly  sensational  turn  to  speculation  about 
life  on  "the  red  planet."  In  that  year  Mars  made 
one  of  its  nearest  approaches  to  the  earth,  and  was 
so  situated  in  its  orbit  that  it  could  be  observed  to 
great  advantage  from  the  northern  hemisphere  of 
the  earth.  The  celebrated  Italian  astronomer,  Schia- 
parelli,  took  advantage  of  this  opportunity  to  make 
a  trigonometrical  survey  of  the  surface  of  Mars — as 
coolly  and  confidently  as  if  he  were  not  taking  his 
sights  across  a  thirty-five-million-mile  gulf  of  empty 
space — and  in  the  course  of  this  survey  he  was  aston- 
ished to  perceive  that  the  reddish  areas,  then  called 
continents,  were  crossed  in  many  directions  by  narrow, 
dusky  lines,  to  which  he  gave  the  suggestive  name  of 
"canals."  Thus  a  kind  of  firebrand  was  cast  into 
the  field  of  astronomical  speculation,  which  has  ever 



since  produced  disputes  that  have  sometimes  ap- 
proached the  violence  of  political  faction.  At  first 
the  accuracy  of  Schiaparelli's  observations  was  con- 
tested; it  required  a  powerful  telescope,  and  the 
most  excellent  "seeing,"  to  render  the  enigmatical 
lines  visible  at  all,  and  many  searchers  were  unable  to 
detect  them.  But  Schiaparelli  continued  his  studies 
in  the  serene  sky  of  Italy,  and  produced  charts  of  the 
gridironed  face  of  Mars  containing  so  much  aston- 
ishing detail  that  one  had  either  to  reject  them  in 
toto  or  to  confess  that  Schiaparelli  was  right.  As 
subsequent  favorable  oppositions  of  Mars  occurred, 
other  observers  began  to  see  the  "canals"  and  to 
confirm  the  substantial  accuracy  of  the  Italian  as- 
tronomer's work,  and  finally  few  were  found  who 
would  venture  to  affirm  that  the  "canals"  did  not 
exist,  whatever  their  meaning  might  be. 

When  Schiaparelli  began  his  observations  it  was 
generally  believed,  as  we  have  said,  that  the  dusky 
areas  on  Mars  were  seas,  and  since  Schiaparelli  thought 
that  the  "canals"  invariably  began  and  ended  at  the 
shores  of  the  "seas,"  the  appropriateness  of  the  title 
given  to  the  lines  seemed  apparent.  Their  artificial 
character  was  immediately  assumed  by  many,  be- 
cause they  were  too  straight  and  too  suggestively 
geometrical  in  their  arrangement  to  permit  the  con- 
clusion that  they  were  natural  watercourses.  A 
most  surprising  circumstance  noted  by  Schiaparelli 
was  that  the  "canals"  made  their  appearance  after 
the  melting  of  the  polar  snow  in  the  corresponding 
hemisphere  had  begun,  and  that  they  grew  darker, 
longer,  and  more  numerous  in  proportion  as  the  polar 



liquidation  proceeded.  Another  very  puzzling  ob- 
servation was  that  many  of  them  became  double  as 
the  season  advanced;  close  beside  an  already  exist- 
ing " canal,'*  and  in  perfect  parallelism  with  it,  an- 
other would  gradually  make  its  appearance.  That 
these  phenomena  actually  existed  and  were  not 
illusions  was  proved  by  later  observations,  and  to-  ' 
day  they  are  seen  whenever  Mars  is  favorably  situated 
for  observation. 

In  the  closing  decade  of  the  nineteenth  century, 
Mr.  Percival  Lowell  took  up  the  work  where  Schia- 
parelli  had  virtually  dropped  it,  and  soon  added  a 
great  number  of  " canals  "  to  those  previously  known, 
so  that  in  his  charts  the  surface  of  the  wonderful 
little  planet  appears  covered  as  with  a  spider's  web, 
the  dusky  lines  criss-crossing  in  every  direction,  with 
conspicuous  knots  wherever  a  number  of  them  come 
together.  Mr.  Lowell  has  demonstrated  that  the  areas 
originally  called  seas,  and  thus  named  on  the  earlier 
charts,  are  not  bodies  of  water,  whatever  else  they 
may  be.  He  has  also  found  that  the  mysterious  lines 
do  not,  as  Schiaparelli  supposed,  begin  and  end  at 
the  edges  of  the  dusky  regions,  but  often  continue 
on  across  them,  reaching  in  some  cases  far  up  into 
the  polar  regions.  But  Schiaparelli  was  right  in  his 
observation  that  the  appearance  of  the  "canals"  is 
synchronous  with  the  gradual  disappearance  of  the 
polar  snows,  and  this  fact  has  become  the  basis  of 
the  most  extraordinary  theory  that  the  subject  of 
life  in  other  worlds  has  ever  given  birth  to. 

Now,  the  effect  of  such  discoveries,  as  we  have 
related,  depends  upon  the  type  of  mind  to  whose 



attention  they  are  called.  Many  are  content  to  ac- 
cept them  as  strange  and  inexplicable  at  present, 
and  to  wait  for  further  light  upon  them;  others  in- 
sist upon  an  immediate  inquiry  concerning  their 
probable  nature  and  meaning.  Such  an  inquiry  can 
only  be  based  upon  inference  proceeding  from  analogy. 
Mars,  say  Mr.  Lowell  and  those  who  are  of  his  opin- 
ion, is  manifestly  a  solidly  incrusted  planet  like  the 
earth;  it  has  an  atmosphere,  though  one  of  great 
rarity;  it  has  water  vapor,  as  the  snows  in  them- 
selves prove ;  it  has  the  alternation  of  day  and  night, 
and  a  succession  of  seasons  closely  resembling  those 
of  the  earth;  its  surface  is  suggestively  divided  into 
regions  of  contrasting  colors  and  appearance,  and 
upon  that  surface  we  see  an  immense  number  of  lines 
geometrically  arranged,  with  a  system  of  symmetri- 
cal intersections  where  the  lines  expand  into  circular 
and  oval  areas — and  all  connected  with  the  annual 
melting  of  the  polar  snows  in  a  way  which  irresistibly 
suggests  the  interference  of  intelligence  directed  to 
a  definite  end.  Why,  with  so  many  concurrent  cir- 
cumstances to  support  the  hypothesis,  should  we  not 
regard  Mars  as  an  inhabited  globe? 

But  the  differences  between  Mars  and  the  earth  are 
in  many  ways  as  striking  as  their  resemblances. 
Mars  is  relatively  small ;  it  gets  less  than  half  as  much 
light  and  heat  as  we  receive;  its  atmosphere  is  so 
rare  that  it  would  be  distressing  to  us,  even  if  we 
could  survive  in  it  at  all;  it  has  no  lakes,  rivers,  or 
seas ;  its  surface  is  an  endless  prairie ;  and  its  ' '  canals ' ' 
are  phenomena  utterly  unlike  anything  on  the  earth. 
Yet  it  is  precisely  upon  these  divergences  between 



the  earth  and  Mars,  this  repudiation  of  terrestrial 
standards,  that  the  theory  of  "life  on  Mars,"  for 
which  Mr.  Lowell  is  mainly  responsible,  is  based. 
Because  Mars  is  smaller  than  the  earth,  we  are  told 
it  must  necessarily  be  more  advanced  in  planetary 
evolution,  the  underlying  cause  of  which  is  the  grad- 
ual cooling  and  contraction  of  the  planet's  mass. 
Mars  has  parted  with  its  internal  heat  more  rapidly 
than  the  earth;  consequently  its  waters  and  its  at- 
mosphere have  been  mostly  withdrawn  by  chemical 
combinations,  but  enough  of  both  yet  remain  to 
render  life  still  possible  on  its  surface.  As  the  globe 
of  Mars  is  evolutionally  older  than  that  of  the  earth, 
so  its  forms  of  organic  life  may  be  proportionally 
further  advanced,  and  its  inhabitants  may  have 
attained  a  degree  of  cultivated  intelligence  much 
superior  to  what  at  present  exists  upon  the  earth. 
Understanding  the  nature  and  the  causes  of  the 
desiccation  of  their  planet,  and  possessing  engineer- 
ing science  and  capabilities  far  in  advance  of  ours, 
they  may  be  conceived  to  have  grappled  with  the 
stupendous  problem  of  keeping  their  world  in  a 
habitable  condition  as  long  as  possible.  Supposing 
them  to  have  become  accustomed  to  live  in  their 
rarefied  atmosphere  (a  thing  not  inconceivable,  since 
men  can  live  for  a  time  at  least  in  air  hardly  less 
rare),  the  most  pressing  problem  for  them  is  that  of 
a  water-supply,  without  which  plant  life  cannot  exist, 
while  animal  life  in  turn  depends  for  its  existence 
upon  vegetation.  The  only  direction  in  which  they 
can  seek  water  is  that  of  the  polar  regions,  where  it  is 
alternately  condensed  into  snow  and  released  in  the 



liquid  form  by  the  effect  of  the  seasonal  changes.  It 
is,  then,  to  the  annual  melting  of  the  polar  snow-fields 
that  the  Martian  engineers  are  supposed  to  have 
recourse  in  supplying  the  needs  of  their  planet,  and 
thus  providing  the  means  of  prolonging  their  own 
existence.  It  is  imagined  that  they  have  for  this 
purpose  constructed  a  stupendous  system  of  irriga- 
tion extending  over  the  temperate  and  equatorial 
regions  of  the  planet.  The  "canals"  represent  the 
lines  of  irrigation,  but  the  narrow  streaks  that  we  see 
are  not  the  canals  themselves,  but  the  irrigated  bands 
covered  by  them.  Their  dark  hue,  and  their  gradual 
appearance  after  the  polar  melting  has  begun,  are 
due  to  the  growth  of  vegetation  stimulated  by  the 
water.  The  rounded  areas  visible  where  several 
"canals"  meet  and  cross  are  called  by  Mr.  Lowell 
"oases."  These  are  supposed  to  be  the  principal 
centres  of  population  and  industry.  It  must  be  con- 
fessed that  some  of  them,  with  their  complicated 
systems  of  radiating  lines,  appear  to  answer  very  well 
to  such  a  theory.  No  attempt  to  explain  them  by 
analogy  with  natural  phenomena  on  the  earth  has 
proved  successful. 

But  a  great  difficulty  yet  remains:  How  explain 
the  seemingly  miraculous  powers  of  the  supposed 
engineers?  Here  recourse  is  had  once  more  to  the 
relative  smallness  of  the  planet.  We  have  remarked 
that  the  force  of  gravity  on  Mars  is  only  thirty-eight 
per  cent,  of  that  on  the  earth.  A  steam -shovel 
driven  by  a  certain  horse-power  would  be  nearly 
three  times  as  effective  there  as  here.  A  man  of  our 
stature  on  Mars  would  find  his  effective  strength  in- 



creased  in  the  same  proportion.  But  just  because  of 
the  slight  force  of  gravity  there,  a  Martian  might 
attain  to  the  traditional  stature  of  Goliath  without 
rinding  his  own  weight  an  encumbrance  to  his  activity, 
while  at  the  same  time  his  huge  muscles  would  come 
into  unimpeded  play,  enabling  him  single-handed  to 
perform  labors  that  would  be  impossible  to  a  whole 
gang  of  terrestrial  workmen.  The  effective  powers 
of  huge  machines  would  be  increased  in  the  same 
way;  and  to  all  this  must  be  added  the  fact  that  the 
mean  density  of  the  materials  of  which  Mars  is  com- 
posed is  much  less  than  that  of  the  constituents  of 
the  earth.  Combining  all  these  considerations,  it 
becomes  much  less  difficult  to  conceive  that  public 
works  might  be  successfully  undertaken  on  Mars 
which  would  be  hopelessly  beyond  the  limits  of  hu- 
man accomplishment. 

Certain  other  difficulties  have  also  to  be  met;  as, 
for  instance,  the  relative  coldness  of  the  climate  of 
Mars.  At  its  distance  it  gets  considerably  less  than 
half  as  much  light  and  heat  as  we  receive.  In  addi- 
tion to  this,  the  rarity  of  its  atmosphere  would 
naturally  be  expected  to  decrease  the  effective  tem- 
perature at  the  planet's  surface,  since  an  atmosphere 
acts  somewhat  like  the  glass  cover  of  a  hot-house  in 
retaining  the  solar  heat  which  has  penetrated  it.  It 
has  been  calculated  that,  unless  there  are  mitigating 
circumstances  of  which  we  know  nothing,  the  aver- 
age temperature  at  the  surface  of  Mars  must  be  far 
below  the  freezing-point  of  water.  To  this  it  is  re- 
plied that  the  possible  mitigating  circumstances 
spoken  of  evidently  exist  in  fact,  because  we  can  see 


that  the  watery  vapor  condenses  into  snow  around 
the  poles  in  winter,  but  melts  again  when  summer 
comes.  The  mitigating  agent  may  be  supposed  to 
exist  in  the  atmosphere  where  the  presence  of  cer- 
tain gases  would  completely  alter  the  temperature 

It  might  also  be  objected  that  it  is  inconceivable 
that  the  Martian  engineers,  however  great  may  be 
their  physical  powers,  and  however  gigantic  the 
mechanical  energies  under  their  control,  could  force 
water  in  large  quantities  from  the  poles  to  the  equator. 
This  is  an  achievement  that  measures  up  to  the  cos- 
mical  standard.  It  is  admitted  by  the  champions  of 
the  theory  that  the  difficulty  is  a  formidable  one; 
but  they  call  attention  to  the  singular  fact  that  on 
Mars  there  can  be  found  no  chains  of  mountains,  and 
it  is  even  doubtful  if  ranges  of  hills  exist  there.  The 
entire  surface  of  the  planet  appears  to  be  almost 
"as  smooth  as  a  billiard  ball,"  and  even  the  broad 
regions  which  were  once  supposed  to  be  seas  apparent- 
ly lie  at  practically  the  same  level  as  the  other  parts, 
since  the  "canals"  in  many  cases  run  uninterrupted- 
ly across  them.  Lowell's  idea  is  that  these  sombre 
areas  may  be  expanses  of  vegetation  covering  ground 
of  a  more  or  less  marshy  character,  for  while  the 
largest  of  them  appear  to  be  permanent,  there  are 
some  which  vary  coincidently  with  the  variations  of 
the  canals. 

As  to  the  kind  of  machinery  employed  to  force  the 
water  from  the  poles,  it  has  been  conjectured  that  it 
may  have  taken  the  form  of  a  gigantic  system  of 
pumps  and  conduits;  and  since  the  Martians  are 



assumed  to  be  so  far  in  advance  of  us  in  their  mastery 
of  scientific  principles,  the  hypothesis  will  at  least  not 
be  harmed  by  supposing  that  they  have  learned  to 
harness  forces  of  nature  whose  very  existence  in  a 
manageable  form  is  yet  unrecognized  on  the  earth. 
If  we  wish  to  let  the  imagination  loose,  we  may  con- 
jecture that  they  have  conquered  the  secret  of  those 
intra-atomic  forces  whose  resistless  energy  is  begin- 
ning to  become  evident  to  us,  but  the  possibility  of 
whose  utilization  remains  a  dream,  the  fulfilment  of 
which  nobody  dares  to  predict. 

Such,  in  very  brief  form,  is  the  celebrated  theory 
of  Mars  as  an  inhabited  world.  It  certainly  capti- 
vates the  imagination,  and  if  we  believe  it  to  repre- 
sent the  facts,  we  cannot  but  watch  with  the  deepest 
sympathy  this  gallant  struggle  of  an  intellectual  race 
to  preserve  its  planet  from  the  effects  of  advancing 
age  and  death.  We  may,  indeed,  wonder  whether 
our  own  humanity,  confronted  by  such  a  calamity, 
could  be  counted  on  to  meet  the  emergency  with 
equal  stoutness  of  heart  and  inexhaustibleness  of 
resource.  Up  to  the  present  time  we  certainly  have 
shown  no  capacity  to  confront  Nature  toe  to  toe,  and 
to  seize  her  by  the  shoulders  and  turn  her  round 
when  she  refuses  to  go  our  way.  If  we  could  get  into 
wireless  telephonic  communication  with  the  Martians 
we  might  learn  from  their  own  lips  the  secret  of  their 
more  than  " Roman  recovery." 



DETWEEN  the  orbits  of  Mars  and  Jupiter  re- 
JD  volves  the  most  remarkable  system  of  little 
bodies  with  which  we  are  acquainted — the  Asteroids, 
or  Minor  Planets.  Some  six  hundred  are  now  known, 
and  they  may  actually  number  thousands.  They 
form  virtually  a  ring  about  the  sun.  The  most  strik- 
ing general  fact  about  them  is  that  they  occupy  the 
place  in  the  sky  which  should  be  occupied,  according 
to  Bode's  Law,  by  a  single  large  planet.  This  fact, 
as  we  shall  see,  has  led  to  the  invention  of  one  of  the 
most  extraordinary  theories  in  astronomy — viz.,  that 
of  the  explosion  of  a  world! 

Bode's  Law,  so-called,  is  only  an  empiric  formula, 
but  until  the  discovery  of  Neptune  it  accorded  so 
well  with  the  distances  of  the  planets  that  astron- 
omers were  disposed  to  look  upon  it  as  really  repre- 
senting some  underlying  principle  of  planetary  dis- 
tribution. They  were  puzzled  by  the  absence  of  a 
planet  in  the  space  between  Mars  and  Jupiter,  where 
the  "law"  demanded  that  there  should  be  one,  and 
an  association  of  astronomers  was  formed  to  search 
for  it.  There  was  a  decided  sensation  when,  in  1801, 
Piazzi,  of  Palermo,  announced  that  he  had  found  a 



little  planet  which  apparently  occupied  the  place  in 
the  system  which  belonged  to  the  missing  body. 
He  named  it  Ceres,  and  it  was  the  first  of  the  Asteroids. 
The  next  year  Olbers,  of  Bremen,  while  looking  for 
Ceres  with  his  telescope,  stumbled  upon  another  small 
planet  which  he  named  Pallas.  Immediately  he  was 
inspired  with  the  idea  that  these  two  planets  were 
fragments  of  a  larger  one  which  had  formerly  occu- 
pied the  vacant  place  in  the  planetary  ranks,  and  he 
predicted  that  others  would  be  found  by  searching 
in  the  neighborhood  of  the  intersection  of  the  orbits 
of  the  two  already  discovered.  This  bold  prediction 
was  brilliantly  fulfilled  by  the  finding  of  two  more — 
Juno  in  1804,  and  Vesta  in  1807.  Olbers  would  seem 
to  have  been  led  to  the  invention  of  his  hypothesis 
of  a  planetary  explosion  by  the  faith  which  astron- 
omers at  that  time  had  in  Bode's  Law.  They  ap- 
pear to  have  thought  that  several  planets  revolving 
in  the  gap  where  the  "law"  called  for  but  one  could 
only  be  accounted  for  upon  the  theory  that  the 
original  one  had  been  broken  up  to  form  the  several. 
Gravitation  demanded  that  the  remnants  of  a  planet 
blown  to  pieces,  no  matter  how  their  orbits  might 
otherwise  differ,  should  all  return  at  stated  periods 
to  the  point  where  the  explosion  had  occurred ;  hence 
Olbers'  prediction  that  any  asteroids  that  might  sub- 
sequently be  discovered  would  be  found  to  have  a 
common  point  of  orbital  intersection.  And  curiously 
enough  all  of  the  first  asteroids  found  practically 
answered  to  this  requirement.  Olbers'  theory  seemed 
to  be  established. 

After  the  first  four,  no  more  asteroids  were  found 



until  1845,  when  one  was  discovered;  then,  in  1847, 
three  more  were  added  to  the  list;  and  after  that 
searchers  began  to  pick  them  up  with  such  rapidity 
that  by  the  close  of  the  century  hundreds  were 
known,  and  it  had  become  almost  impossible  to  keep 
track  of  them.  The  first  four  are  by  far  the  largest 
members  of  the  group,  but  their  actual  sizes  remained 
unknown  until  less  than  twenty  years  ago.  It  was 
long  supposed  that  Vesta  was  the  largest,  because  it 
shines  more  brightly  than  any  of  the  others;  but 
finally,  in  1895,  Barnard,  with  the  Lick  telescope, 
definitely  measured  their  diameters,  and  proved  to 
everybody's  surprise  that  Ceres  is  really  the  chief, 
and  Vesta  only  the  third  in  rank.  His  measures  are 
as  follows:  Ceres,  477  miles;  Pallas,  304  miles; 
Vesta,  239  miles;  and  Juno,  120  miles.  They  differ 
greatly  in  the  reflective  power  of  their  surfaces,  a 
fact  of  much  significance  in  connection  with  the 
question  of  their  origin.  Vesta  is,  surface  for  surface, 
rather  more  than  three  times  as  brilliant  as  Ceres, 
whence  the  original  mistake  about  its  magnitude. 

Nowadays  new  asteroids  are  found  frequently  by 
photography,  but  physically  they  are  most  insignifi- 
cant bodies,  their  average  diameter  probably  not  ex- 
ceeding twenty  miles,  and  some  are  believed  not  to 
exceed  ten.  On  a  planet  only  ten  miles  in  diameter, 
assuming  the  same  mean  density  as  the  earth's, 
which  is  undoubtedly  too  much,  the  force  of  gravity 
would  be  so  slight  that  an  average  man  would  not 
weigh  more  than  three  ounces,  and  could  jump  off 
into  space  whenever  he  liked. 

Although  the  asteroids  all  revolve  around  the  sun 



in  the  same  direction  as  that  pursued  by  the  major 
planets,  their  orbits  are  inclined  at  a  great  variety 
of  angles  to  the  general  plane  of  the  planetary  system, 
and  some  of  them  are  very  eccentric — almost  as  much 
so  as  the  orbits  of  many  of  the  periodic  comets.  It 
has  even  been  conjectured  that  the  two  tiny  moons 
of  Mars  and  the  four  smaller  satellites  of  Jupiter 
may  be  asteroids  gone  astray  and  captured  by  those 
planets.  Two  of  the  asteroids  are  exceedingly  re- 
markable for  the  shapes  and  positions  of  their  orbits ; 
these  are  Eros,  discovered  in  1898,  and  T.  G.,  1906, 
found  eight  years  later.  The  latter  has  a  mean  dis- 
tance from  the  sun  slightly  greater  than  that  of 
Jupiter,  while  the  mean  distance  of  Eros  is  less  than 
that  of  Mars.  The  orbit  of  Eros  is  so  eccentric  that 
at  times  it  approaches  within  15,000,000  miles  of  the 
earth,  nearer  than  any  other  regular  member  of  the 
solar  system  except  the  moon,  thus  affording  an  un- 
rivalled means  of  measuring  the  solar  parallax.  But 
for  our  present  purpose  the  chief  interest  of  Eros  lies 
in  its  extraordinary  changes  of  light. 

These  changes,  although  irregular,  have  been  ob- 
served and  photographed  many  times,  and  there 
seems  to  be  no  doubt  of  their  reality.  Their  signifi- 
cance consists  in  their  possible  connection  with  the 
form  of  the  little  planet,  whose  diameter  is  generally 
estimated  at  not  more  than  twenty  miles.  Von 
Oppolzer  found,  in  1901,  that  Eros  lost  three-fourths 
of  its  brilliancy  once  in  every  two  hours  and  thirty- 
eight  minutes.  Other  observers  have  found  slightly 
different  periods  of  variability,  but  none  as  long  as 
three  hours.  The  most  interesting  interpretation 



that  has  been  offered  of  this  phenomenon  is  that  it  is 
due  to  a  great  irregularity  of  figure,  recalling  at  once 
Gibers'  hypothesis.  According  to  some,  Eros  may 
be  double,  the  two  bodies  composing  it  revolving 
around  each  other  at  very  close  quarters;  but  a  more 
striking,  and  it  may  be  said  probable,  suggestion  is 
that  Eros  has  a  form  not  unlike  that  of  a  dumb-bell, 
or  hour-glass,  turning  rapidly  end  over  end  so  that 
the  area  of  illuminated  surface  presented  to  our  eyes 
continually  changes,  reaching  at  certain  times  a 
minimum  when  the  amount  of  light  that  it  reflects 
toward  the  earth  is  reduced  to  a  quarter  of  its  maxi- 
mum value.  Various  other  bizarre  shapes  have  been 
ascribed  to  Eros,  such,  for  instance,  as  that  of  a 
flat  stone  revolving  about  one  of  its  longer  axes,  so 
that  sometimes  we  see  its  face  and  sometimes  its 

All  of  these  explanations  proceed  upon  the  as- 
sumption that  Eros  cannot  have  a  simple  globular 
figure  like  that  of  a  typical  planet,  a  figure  which  is 
prescribed  by  the  law  of  gravitation,  but  that  its 
shape  is  what  may  be  called  accidental;  in  a  word, 
it  is  a,  fragment,  for  it  seems  impossible  to  believe  that 
a  body  formed  in  interplanetary  space,  either  through 
nebular  condensation  or  through  the  aggregation  of 
particles  drawn  together  by  their  mutual  attractions, 
should  not  be  practically  spherical  in  shape.  Nor  is 
Eros  the  only  asteroid  that  gives  evidence  by  varia- 
tions of  brilliancy  that  there  is  something  abnormal 
in  its  constitution;  several  others  present  the  same 
phenomenon  in  varying  degrees.  Even  Vesta  was 
regarded  by  Olbers  as  sufficiently  variable  in  its  light 


to  warrant  the  conclusion  that  it  was  an  angular  mass 
instead  of  a  globe.  Some  of  the  smaller  ones  show 
very  notable  variations,  and  all  in  short  periods,  of 
three  or  four  hours,  suggesting  that  in  turning  about 
one  of  their  axes  they  present  a  surface  of  variable 
extent  toward  the  sun  and  the  earth. 

The  theory  which  some  have  preferred  that  the 
variability  of  light  is  due  to  the  differences  of  reflect- 
ive power  on  different  parts  of  the  surface  would, 
if  accepted,  be  hardly  less  suggestive  of  the 
origin  of  these  little  bodies  by  the  breaking  up  of  a 
larger  one,  because  the  most  natural  explanation  of 
such  differences  would  seem  to  be  that  they  arose 
from  variations  in  the  roughness  or  smoothness  of 
the  reflecting  surface,  which  would  be  characteristic 
of  fragmentary  bodies.  In  the  case  of  a  large  planet 
alternating  expanses  of  land  and  water,  or  of  vegeta- 
tion and  desert,  would  produce  a  notable  variation 
in  the  amount  of  reflection,  but  on  bodies  of  the  size 
of  the  asteroids  neither  water  nor  vegetation  could 
exist,  and  an  atmosphere  would  be  equally  im- 

One  of  the  strongest  objections  to  Olbers'  hypoth- 
esis is  that  only  a  few  of  the  first  asteroids  discovered 
travel  in  orbits  which  measurably  satisfy  the  re- 
quirement that  they  should  all  intersect  at  the  point 
where  the  explosion  occurred.  To  this  it  was  at  first 
replied  that  the  perturbations  of  the  asteroidal  orbits, 
by  the  attractions  of  the  major  planets,  would  soon 
displace  them  in  such  a  manner  that  they  would 
cease  to  intersect.  One  of  the  first  investigations 
tmclertaken  by  the  late  Prof.  Simon  Newcomb  was 



directed  to  the  solution  of  this  question,  and  he  ar- 
rived at  the  conclusion  that  the  planetary  perturba- 
tions could  not  explain  the  actual  situation  of  the 
asteroidal  orbits.  But  afterward  it  was  pointed  out 
that  the  difficulty  could  be  avoided  by  supposing 
that  not  one  but  a  series  of  explosions  had  produced 
the  asteroids  as  they  now  are.  After  the  primary 
disruption  the  fragments  themselves,  according  to 
this  suggestion,  may  have  exploded,  and  then  the 
resulting  orbits  would  be  as  "tangled"  as  the  heart 
could  wish.  This  has  so  far  rehabilitated  the 
explosion  theory  that  it  has  never  been  entirely 
abandoned,  and  the  evidence  which  we  have  just 
cited  of  the  probably  abnormal  shapes  of  Eros  and 
other  asteroids  has  lately  given  it  renewed  life.  It 
is  a  subject  that  needs  a  thorough  rediscussion. 

We  must  not  fail  to  mention,  however,  that  there 
is  a  rival  hypothesis  which  commends  itself  to  many 
astronomers — viz.,  that  the  asteroids  were  formed  out 
of  a  relatively  scant  ring  of  matter,  situated  between 
Mars  and  Jupiter  and  resembling  in  composition  the 
immensely  more  massive  rings  from  which,  according 
to  Laplace's  hypothesis,  the  planets  were  born.  It 
is  held  by  the  supporters  of  this  theory  that  the  at- 
traction of  the  giant  Jupiter  was  sufficient  to  prevent 
the  small,  nebulous  ring  that  gave  birth  to  the 
asteroids  from  condensing  like  the  others  into  a  single 

But  if  we  accept  the  explosion  theory,  with  its  cor- 
ollary that  minor  explosions  followed  the  principal 
one,  we  have  still  an  unanswered  question  before  us: 
What  caused  the  explosions?  The  idea  of  a  world 


blowing  up  is  too  Titanic  to  be  shocking;  it  rather 
amuses  the  imagination  than  seriously  impresses  it; 
in  a  word,  it  seems  essentially  chimerical.  We  can  by 
no  appeal  to  experience  form  a  mental  picture  of 
such  an  occurrence.  Even  the  moon  did  not  blow 
up  when  it  was  wrecked  by  volcanoes.  The  ex- 
plosive nebulas  and  new  stars  are  far  away  in  space, 
and  suggest  no  connection  with  such  a  catastrophe 
as  the  bursting  of  a  planet  into  hundreds  of  pieces. 
We  cannot  conceive  of  a  great  globe  thousands  of 
miles  in  diameter  resembling  a  pellet  of  gunpowder 
only  awaiting  the  touch  of  a  match  to  cause  its  sud- 
den disruption.  Somehow  the  thought  of  human 
agency  obtrudes  itself  in  connection  with  the  word 
" explosion,"  and  we  smile  at  the  idea  that  giant 
powder  or  nitro-glycerine  could  blow  up  a  planet. 
Yet  it  would  only  need  enough  of  them  to  do  it. 

After  all,  we  may  deceive  ourselves  in  thinking,  as 
we  are  apt  to  do,  that  explosive  energies  lock  them- 
selves up  only  in  small  masses  of  matter.  There  are 
many  causes  producing  explosions  in  nature  |  every 
volcanic  eruption  manifests  the  activity  of  some  of 
them.  Think  of  the  giant  power  of  confined  steam; 
if  enough  steam  could  be  suddenly  generated  in  the 
centre  of  the  earth  by  a  downpour  of  all  the  waters 
of  the  oceans,  what  might  not  the  consequences  be 
for  our  globe?  In  a  smaller  globe,  and  it  has  never 
been  estimated  that  the  original  asteroid  was  even 
as  large  as  the  moon,  such  a  catastrophe  would,  per- 
haps, be  more  easily  conceivable;  but  since  we  are 
compelled  in  this  case  to  assume  that  there  was  a 
series  of  successive  explosions,  steam  would  hardly 



answer  the  purpose;  it  would  be  more  reasonable 
to  suppose  that  the  cause  of  the  explosion  was  some 
kind  of  chemical  reaction,  or  something  affecting  the 
atoms  composing  the  exploding  body.  Here  Dr. 
Gustav  Le  Bon  comes  to  our  aid  with  a  most  startling 
suggestion,  based  on  his  theory  of  the  dissipation  of 
intra-atomic  energy.  It  will  be  best  to  quote  him 
at  some  length  from  his  book  on  The  Evolution  of 

"It  does  not  seem  at  first  sight,'*  says  Doctor  Le 
Bon,  "very  comprehensible  that  worlds  which  ap- 
pear more  and  more  stable  as  they  cool  could  become 
so  unstable  as  to  afterward  dissociate  entirely.  To 
explain  this  phenomenon,  we  will  inquire  whether 
astronomical  observations  do  not  allow  us  to  witness 
this  dissociation. 

"We  know  that  the  stability  of  a  body  in  motion, 
such  as  a  top  or  a  bicycle,  ceases  to  be  possible  when 
its  velocity  of  rotation  descends  below  a  certain 
limit.  Once  this  limit  is  reached  it  loses  its  stability 
and  falls  to  the  ground.  Prof.  J.  J.  Thomson  even 
interprets  radio-activity  in  this  manner,  and  points 
out  that  when  the  speed  of  the  elements  composing 
the  atoms  descends  below  a  certain  limit  they  be- 
come unstable  and  tend  to  lose  their  equilibria. 
There  would  result  from  this  a  commencement  of 
dissociation,  with  diminution  of  their  potential  energy 
and  a  corresponding  increase  of  their  kinetic  energy 
sufficient  to  launch  into  space  the  products  of  intra- 
atomic  disintegration. 

"It  must  not  be  forgotten  that  the  atom  being  an 
enormous  reservoir  of  energy  is  by  this  very  fact 



comparable  with  explosive  bodies.  These  last  re- 
main inert  so  long  as  their  internal  equilibria  are 
undisturbed.  So  soon  as  some  cause  or  other  modi- 
fies these,  they  explode  and  smash  everything  around 
them  after  being  themselves  broken  to  pieces. 

"Atoms,  therefore,  which  grow  old  in  consequence 
of  the  diminution  of  a  part  of  their  intra-atomic 
energy  gradually  lose  their  stability.  A  moment, 
then,  arrives  when  this  stability  is  so  weak  that  the 
matter  disappears  by  a  sort  of  explosion  more  or  less 
rapid.  The  bodies  of  the  radium  group  offer  an 
image  of  this  phenomenon — a  rather  faint  image,  how- 
ever, because  the  atoms  of  this  body  have  only 
reached  a  period  of  instability  when  the  dissociation 
is  rather  slow.  It  probably  precedes  another  and 
more  rapid  period  of  dissociation  capable  of  produc- 
ing their  final  explosion.  Bodies  such  as  radium, 
thorium,  etc.,  represent,  no  doubt,  a  state  of  old  age 
at  which  all  bodies  must  some  day  arrive,  and  which 
they  already  begin  to  manifest  in  our  universe,  since 
all  matter  is  slightly  radio-active.  It  would  suffice 
for  the  dissociation  to  be  fairly  general  and  fairly 
rapid  for  an  explosion  to  occur  in  a  world  where  it 
was  manifested. 

"  These  theoretical  considerations  find  a  solid  sup- 
port in  the  sudden  appearances  and  disappearances 
of  stars.  The  explosions  of  a  world  which  produce 
them  reveal  to  us,  perhaps,  how  the  universes  perish 
when  they  become  old. 

"As  astronomical  observations  show  the  relative 
frequency  of  these  rapid  destructions,  we  may  ask 
ourselves  whether  the  end  of  a  universe  by  a  sudden 



explosion   after  a  long  period  of  old  age  does  not 
represent  its  most  general  ending." 

Here,  perhaps,  it  will  be  well  to  stop,  since,  entran- 
cing as  the  subject  may  be,  we  know  very  little  about 
it,  and  Doctor  Le  Bon's  theory  affords  a  limitless 
field  for  the  reader's  imagination. 


AEORLITES,  study  of,  197. 

Alcor,  58,  59. 

Alcyone,  37,  41,  42. 

Aldebaran,  62,  86. 

Alioth,  58,  59,  60. 

Alpha  Centauri,  46,  66. 

Alpha  Herculis,  86. 

Alnilam,  64. 

Alnita,   64. 

Anderson,  Rev.  Doctor,  dis- 
covers Nova  Persei,  75. 

Andromeda  Nebula,  75,  91,  99, 
100,  103,  104,  192. 

Antares,  86. 

Arcturus,  8,  44,  46,  66,  68. 

Arrhenius,  Svante,  theory,  139, 
142,  143,  154,  158,  160,  184. 

Aso  San,  crater,  219. 

Asteroids,  the,  29,  252. 

Atlas,  37. 

Auriga,  75. 

Aurora  Australis,  148. 

Aurora  Borealis,  147,  148,  154, 
157,  160. 

BAILY,   FRANCIS,   quoted,    117, 


Belt,  Orion's,  64. 
Benetnasch,   58,   59,  60. 
Betelgeuse,  64,  86. 
Biela's    comet,    180,    191,    192, 


Brooks'  comet,   176,   181. 
"  Black  stone,"  the,  196. 
Bode's  Law,  254,  255. 
Bredichin,  researches,  184. 

CANCER,  55. 
Canopus,  68. 
Canyon  Diablo  meteors,  202, 


Capella,  75,  76. 
Cassiopeia,  24,  56,  61,  69. 
Catharina,  crater,  230. 
Centaurus,   14,  30. 
Ceres,  255,  256. 
Cetus,  86,  99. 
Chamberlin,   Professor,   theory, 


Chi  Persei,  24. 
Clavius,  crater,  230. 
Clerke,    Agnes    M.,    quoted,    8, 


Coal-sack,  the,  2,  3,  4,  7,  13. 

Comet,  Halley's,  165;  Swift's, 
167;  phenomena,  169;  ap- 
proach to  the  sun,  170;  of 
1811,  171;  of  1882,  171,  174, 
175;  their  light,  171;  of  1908, 
172;  of  1729,  172;  of  1843, 
173,  174,  175;  of  1858,  173; 
of  1861,  173;  of  1880,  174; 
of  1668,  175;  and  photog- 
raphy, 176;  Brooks',  176; 
Daniels',  176;  of  1770,  179; 
family,  180;  Biela's,  180, 
191,  192,  195;  tails,  183,  184; 
of  1744,  185;  disintegration, 

Comstock,  George  C.,  theory, 
20,  33. 

Coon  Butte  Meteorite,  202,  204, 
211,  212. 



Corona,  113,  144,  117,  118,  119, 
124,  125,  130,  138. 

Coronium,   124. 

Corvus,  62. 

Craters,  lunar,  216,  219-221; 
Tycho,  216,  219;  Theophilus, 
219,  230;  Cyrillus,  230;  Catha- 
rina,  230;  Longomontanus, 
230;  Wilhelm  I.,  230;  Clavius, 

Cygnus,  8,  38,  62,  73,  74. 

Cyrillus  Crater,  230. 

DANIELS'  comet,  176. 

Delphinus,  62. 

Denning,  W.  F.,  researches, 

Diamonds  in  meteorites,  202. 

Donati's  comet,  173,  184. 

Dubhe,   58,  59,  60. 

Dyson,  Professor,  investiga- 
tions, 50,  51. 

EARTH,  course,  47,  49;  magnet, 

148,   157- 

Eclipse,  of  the  sun,  113,  114; 
of  1842,  114,  117,  118;  of 
1900,  118,  125;  of  1905,  118. 

Eddington,  Professor,  investiga- 
tions, 50. 

Electra,  37. 

Eros,  257,  258. 

FIXED  stars,  39,  40,  41. 
Forbes,    Prof.    George,    theory, 

GALAXY,  the,  2,  3,  7,  12,  13,  17, 

18,  19,  23. 

"  Gegenschein,"  136,  137,  142. 
Gemini,  62,  91. 
Gilbert,  W.  K.,  on  lunar  craters, 


Great  Dipper,  the,  49,  57,  58. 
Great  Southern  Comet,  174. 
Great  Square  of  Pegasus,   62. 
Groombndge,     1830,      motion, 


HALE,  PROFESSOR,  and  sun- 
spots,  123. 

Halley's  comet,  48,   165. 

Helium,  201. 

Hercules,   14,  25,  30,  46. 

Herschel,  Alexander,  and  meteor 
swarms,  188. 

Herschel,  Sir  William,  observa- 
tions, 2,  7,  26,  30,  243. 

Hyades,  22,  62. 

Hydra,  62. 

IZAMAL,  temples,  54,  55. 

JANSSEN,    PROFESSOR,    theory, 

84,  85. 

Juno,  255,  256. 
Jupiter,  29,  40,   166,   179,   180 

191,  241. 

KAPPA,  69. 

Kapteyn,  Professor,  investi- 
gations, 50. 

Keeler,  Professor,  discovery,  88. 
Kepler's  star,  74. 

LAPLACE,    PROFESSOR,    theory, 

103,  109,  in. 
Le  Bon,  Dr.  Gustav,  theory,  86; 

quoted,  260. 
Leo,  62,   187. 
Lexell's  comet,  179,  180. 
Longomontanus,      crater  -  ring, 

Lowell,   Percival,  observations, 


Lunar  Apennines,  225. 
Lunar  Caucasus,  225. 
Lyra,  88. 

MAEDLER,  theory,  41. 
Magellanic  clouds,  24. 
Magnetic  storms,  126,  151,  152. 
Maia,  37. 

Mare  Cnsium,  235. 
Mare  Imbrium,  the,   225. 
Mare  Serenitatis,  the,  225. 
Mare  Tranquilitatis,  the,  229. 



Mars,  and  the  Asteroids,  29; 
distance  from  earth,  214;  de- 
scription, 241,  242;  habit- 
ability,  243;  canals,  244,  247; 
resemblance  to  the  earth, 
248;  life  on,  249-253. 

Maunder,  E.  W.,  quoted,  133. 

Megrez,  58,  59,  60. 

Merak,  58,  59,  60. 

Mercury,  234,  240. 

Merope,  37. 

Meteorites,  study  of,  197;  veloc- 
ity, 198,  208;  stone  and  iron, 
201,  202,  203;  fall  of,  203; 
Peary's,  208;  origin,  222. 

Meteors,  showers,  186,  187; 
swarms,  188;  November,  191; 
of  ancient  times,  196;  Canyon 
Diablo,  202,  204,  211. 

Milky  Way,  the,  2,  3,  4,  8,  9, 

12,    17,     l8,     19,    2O,    21,    42. 

Mintaka,  64. 

Mira  Ceti,  86,   123. 

Mizar,  58,  59,  60. 

Moissan  diamonds,  202. 

Moon,  the,  distance  from  earth, 
214;  former  conditions,  215; 
craters  of,  216,  219-221;  sea- 
beds,  225-229. 

Morehouse's  comet,   172. 

Moulton,  Professor,  theory,  107. 

NEBULA,  Andromeda,  103,  104; 

Orion,   103,   104. 
Nebula,  Trifid,  7;  dark,  10,  12; 

in  Orion,  30;  Pleiades,  34. 
Nebula  in  Cetus,  101. 
Neptune,  241. 
Neptune,  speed,  40. 
Northern  Cross,  62. 
Northern  Crown,  61,  63,  74,  84. 
Northern  Lights,    148,    158. 
Nova  Persei,  71,  75,  80,  81,  83, 

84,  85,  86. 

OLBER'S  theory,  29,  253,  257. 
Olmstead,    Prof.    Denison,    and 
meteors,  186,  187. 

Omega  Centauri,  30,  33. 

Ophiuchus,  74. 

Orion,  22,  37,  55,  63,  103,  104. 

PALLADIUM,  the,    196. 

Pallas,  255,  256. 

Perrine,  discovery,  33. 

Perseus,   24,   56,   75. 

Phaed,   58,   59,   60. 

Pickering,     Prof.     W.     H.,     on 

meteors,  211,  212. 
Planetesimal    Hypothesis,    107, 

108,   in. 

Planets,  the,  39,  40,  239-241. 
Pleiades,  23,  34,  37,  49,  62. 
Pointers,  the,  59. 

Rigel,  64,  86. 

Rosse,  Lord,  Whirlpool  Nebula, 
88,  89;  spiral  nebulas,  92. 


Saturn,   191,  241. 

Schiaparelli,  discovery,  243,  244. 

Scorpio,  4,   7,   55. 

Sea  of  Serenity,  the,  225,  226. 

Sea  of  Showers,  the,  225. 

Sea  of  Tranquility,  the,  229. 

Seeliger,  Professor,  theory,  80. 

Sickle,  the,  62. 

Sirius,  44,  46,  66,  86,  202. 

Southern  Cross,  3,  64,  65. 

Spiral  nebulae,   112. 

Star,  clouds,  23,  24,  50;  swarms, 
24,  25,  50;  clusters,  25-34, 
50;  fixed,  39,  40  ;  motions, 
43,  44,  45,  48-52;  tracks,  47, 
48,  49;  drift,  49,  50. 

Stars,  speeding,  43,  44;  tem- 
porary, 68,  69,  73,  74,  86. 

Stones,  showers,   196,   197. 

Sun,  eclipse,  113;  surroundings, 
113;  prominences,  113,  119, 
120,  124;  spots,  123,  124,  127, 
151,  154,  158;  a  variable  star, 

Swan,  the,  4. 



TAURUS,  62. 

Taygeta,  37. 

Theophilus,  crater,  219,  230. 

Tidal  explosion,   108. 

Tides  in  couples,   107. 

Triangulum,  96,  99,  100. 

Trifid  Nebula,  7. 

Twins,  the,  62. 

Tycho,  crater,  216,  219. 

Tycho's  Star,  69,  70,  71,  73. 

URANUS,  188,  241. 
Ursa  Major,  57,  97,  99. 

VEGA,  46,  £6. 
Venus,  70,  240. 
Vesta,  255,  256,  258. 

WHIRLPOOL  NEBULA,  Rosse's,  88. 
Wilhelm  I.,  crater-ring,  230. 
Wolf,  Rudolph,  discovery,  151. 

YOUNG,  PROFESSOR,  coronium, 

ZODIACAL  LIGHT,  the,  131-143. 
Zurich  Chronicles,  ancient,  151. 


14  DAY  USE 


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